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11 Feeding Behavior and General Considerations for Feeding Management FEEDING BEHAVIOR (fat) during colder weather conditions rather than increasing voluntary feed intake in times of poor feed supply (Loudon Equine feeding behavior affects feed intake and feeding et al., 1989; Rhind et al., 1998). management of horses. Horses are herbivores; therefore, Some semblance of the eat-for-energy maxim was evi- they may require a forage supply to lessen the risks of clin- dent in ponies fed pelleted diets whose energy content was ical disorders such as colic (Archer and Proudman, 2005), diluted by adding sawdust (Laut et al., 1985). Ponies re- laminitis (Rowe et al., 1994), and oral and locomotory be- sponded to the dietary caloric dilution by increasing their havioral problems (Mills et al., 2005). By acknowledging total daily feed intake and thereby maintained energy intake the normal feeding behaviors of the equine, appropriate feed until gut capacity became limiting (Laut et al., 1985). How- management decisions can be made to minimize these im- ever, voluntary energy intake can be greatly distorted by the portant clinical problems and contribute to the well-being of palatability and composition of the diet. When offered, the horse. The following discussion is not intended to be a Thoroughbred and Standardbred racehorses consumed comprehensive treatise on equine behavior, which can be about 1.58 to 1.76 kg concentrate/100 kg BW, representing found in books by Waring (2002), McGreevy (2004), and about 65â71 percent of total feed intake (Southwood et al., Mills and McDonnell (2005). 1993). Young pony mares (average weight 238 kg) fed a 60 percent grass hayâ40 percent concentrate mix as a chaff or pellet ate excessive amounts of diet and, hence, energy for Energy Balance 6â7 weeks (peak intake of 4.5 kg DM/100 kg BW), with the A commonly held nutritional maxim is that horses eat to result that all mares gained considerable weight (45 kg over meet their energy requirements. In actuality, patterns of sea- 4 weeks) (Argo et al., 2002). Following this period of greed, sonal feed intake plotted against weight gain or body weight the mares self-limited their feed consumption to mainte- (BW) have not totally upheld this concept. The body nance energy amounts resulting in no further weight gain. weightâtime plots of pastured Przewalskiâs horses and ma- This overindulgence of palatable feeds occurs despite the ture and young Quarter horse mares (Berger et al., 1999; risk of clinical disorders (colic, laminitis) (Rowe et al., Fitzgerald and McManus, 2000) showed increasing weight 1994; Tinker et al., 1997; Cohen et al., 1999; Hudson et al., gains through spring, reaching a maximum weight in sum- 2001). mer, followed by progressive weight loss through the au- Dulphy et al. (1997a,b) summarized forage intakes by tumn and winter. Weight gains through spring and summer horses and found a considerable range of voluntary intakes averaged about 0.5 kg/d, followed by similar weight loss of hays by horses. Based on 17 INRA studies and 42 pub- through autumn and winter. A high feeding rate coincided lished papers, Dulphy et al. (1997b) provided summary data with low body weight in spring, followed by low feeding ac- that showed that lucerne (alfalfa) hay was consumed at av- tivity during peak body weights in summer with a return to erage rates of 2.24â2.44 kg/100 kg BW (range 2â2.7), high feeding activity in autumn and winter (Berger et al., amounts that were higher than average voluntary feed intake 1999). The study did not determine if weight loss in autumn (VFI) of some grass hays (2.01â2.12 kg/100 BW; range and winter was due to poor quality feed, a reduction in vol- 1.3â2.7) and/or straws (1.28 kg/100 kg BW; range 0.9â1.8) untary feed intake, or cold weather extremes. Similar body (Dulphy et al., 1997b). In a separate study, barley straw and weightâtime patterns are typical of wild ruminants, which maize silage had a low acceptability by horses and were deposit fat and soft tissue in summer and use stored energy eaten in small amounts (< 1 kg/100 kg BW) despite provid- 211
212 NUTRIENT REQUIREMENTS OF HORSES ing subnormal energy intakes (Dulphy et al., 1997a). Evi- level (Goold, 1991), which can cause considerable pressure dently, simply providing feed to a horse is not sufficient to on palatable species and which, if sustained, can lead to the make the horse eat it, but providing palatable feed ad libitum disappearance of the preferred species from the sward may contribute to undesired consequences. (Archer, 1973; Wallace, 1977; Archer, 1978a,b; Elphinstone, 1981). Studies on pasture species preference by equines have yielded inconsistent results, and this may at least in Typical Feeding Behavior part reflect differences in the maturity of the herbage at the time of study. As plants mature, they become less palatable. Foals Fleurance et al. (2001) suggested that horses selected Damâs milk is the main source of nutrients for the new- herbage on the basis of stage of growth rather than botanical born foal. Normal foals began suckling within 1 to 2 hours species. As a consequence, differential maturation rates be- after birth (Kubiak et al., 1988; Houpt, 2002) and nursed 10 tween species may result in those which mature rapidly times an hour to 1 day old, gradually decreasing this rate being selected less frequently as the season advances in to 1.5 bouts/h by 17 weeks of age (Smith-Funk and Crowell- favor of those which mature more slowly (McMeniman, Davis, 1992). Successful suckling bouts by mule foals lasted 2003). In addition to changes in acceptance with seasonal 47â54 seconds regardless of age (Smith-Funk and Crowell- changes in plant development, palatability is affected by Davis, 1992), compared to 57â79 seconds for Thoroughbred plant nutrient status, which is under environmental influ- foals (Cameron et al., 1999). The average daily time spent ence. Nevertheless, despite the difficulties of interpreting nursing by Thoroughbred foals was 46 minutes (range data of studies on species preference by horses due to the 27â78 minutes) and milk consumption, estimated by using dynamic nature of herbage palatability, it has generally been isotope dilution methods, was determined to be 14.7 kg found that pastures of mixed species were preferred to milk/d (Cameron et al., 1999). monocultures (Archer, 1973) and grasses were preferred to Feral neonates suckled for 6â8 percent of the day, then legumes and herbs (Archer, 1973; Odberg and Francis- rapidly decreased time spent suckling to 2.3 percent of the Smith, 1976; Archer, 1978a,b; Rogalski, 1982, 1984a; Kry- day over the next 8 weeks, plateaued at 2 percent of the day syl et al., 1984; Chenost and Martin-Rosset, 1985). Re- until week 29, and self-weaned at week 35 (Duncan et al., ported palatable cool-season pasture species for horses 1984). Some foals started eating solid feeds as early as 1 day include perennial ryegrass (Lolium perenne), meadow fes- of age, although 1-week-old foals spent only about 8 percent cue (Festuca pratensis), timothy (Phleum pratense), or- of the day eating solid feed (Crowell-Davis et al., 1985; chardgrass (Dactylis glomerata), creeping red fescue (F. Boyd, 1988). By 21 weeks, foals spent 47 percent of day- rubra), white bent (Agrostis gigantea), smooth stalked light hours eating solid feeds. Similarly, feral foals were re- meadow grass, Italian ryegrass (Lolium multiflorum), hybrid ported to spend only 18â25 percent of the day grazing at 2â4 ryegrass (L. perenne Ã multiflorum), tall fescue (F. arundi- weeks old, then 42â45 percent by 20â28 weeks of age, and nacea), Kentucky bluegrass (Poa pratensis), and smooth up to 73 percent at 5 months of age (Duncan et al, 1984; brome grass (Bromus inermis). Other pasture species ac- Boyd, 1988). Dams allowed their foals to eat grain with ceptable to horses include several cereals grown as forage them (Boyd, 1991), which is a behavior that can be ex- crops such as barley (Hordeum vulgare) and oats (Avena ploited to introduce foals to grain and/or other solid feeds. sativa). Legumes in horse pastures may include red and Foals confined with their dams in box stalls will learn rela- white clover (Trifolium pratense, T. repens), strawberry tively quickly to consume grain mixes and hays. Realisti- clover (T. fragiferum), sainfoin (Onobrychis vicifolia), al- cally, foals kept continuously on pasture with their dams are falfa (Medicago sativa), and vetch (Vicia atropurpurea). unlikely to consume much grain or hay. Coleman et al. Herbs such as dandelion (Taraxacum officinale), ribgrass (1999) reported that 2-month-old foals, whose dams were (Plantago lanceolata), and chicory (Cichorium intybus) grazing good-quality pastures, ate only 48â75 percent of the may also be eaten. Warm-season species include Bermuda- 0.9â1.35 kg creep feed offered to them daily. grass (Cynadon dactylon), crabgrass (Digitaria spp.), East- ern gamagrass (Tripsacum dactyloides), blue couch (Digi- taria didactylis), bahiagrass (Paspalum notatum), Rhodes Mature Horses on Pasture grass (Chloris gayana), setaria (Setaria anceps), elephant- Forages are the main component of feral horse diets. Typ- grass (Pennisetum purpureum), pearl millet (Pennisetum ically, the forage diets consumed by feral horses have con- glaucum), Kikuyu grass (Pennisetum clandestinum), pas- siderable variety: 65 percent grasses and sedges, 25 percent palum (Paspalum dilantatum), prairiegrass (Bromus spp.), shrubs, and minor amounts of forbs (Salter and Hudson, India grass (Sorgastrum nutans L.), switchgrass (Panicum 1979; Krysyl et al., 1984). This feral horse preference for virgatum L.), big bluestem (Andropogon geradi), matua variety has been shown to be mimicked by domesticated bromegrass (Bromus willdenowii), altai wildrye (Leysum an- horses (see below; Goodwin et al., 2005a). Horses are gustus Trin), crested wheatgrass (Agrypynon cristatum), and highly selective grazers and have grazed pastures to ground reed canarygrass (Phalaris arundinaceae) (Archer, 1973;
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 213 Rogalski, 1977, 1984b; Templeton, 1979; Elphinstone, 1981; seasonally dependent. Horses spent more time in nocturnal Falkowski et al., 1983; Williams, 1987; Gallagher and Mc- feeding in summer than winter (Kaseda, 1983). Meniman, 1988; Hunt, 1991; McCann and Hoveland, 1991; Feral horses in Alberta spent nearly 75 percent of the day Lieb et al., 1993; Almeida et al., 1999; Friend and Nash, in foraging activities (Salter and Hudson, 1979), while Ca- 2000; Guay et al., 2002). Further information on the relative margue mares spent 71 percent of daylight hours and 49â56 intakes and nutritive value of some of these species is given percent of nighttime hours (sunset to sunrise) grazing during in Chapter 8, Tables 8.1â8.4. winter and spring (Duncan, 1985). Ponies in Iceland and There have been a number of reports on sward height Thoroughbred geldings in Scotland spent 62 percent time preferences by grazing horses, which have yielded conflict- grazing, 12â29 percent resting, and 9 percent walking on ing results. Although horses showed a distinct preference for late-summer pastures (Marsden, 1993; Magnusson and timothygrass swards of 5 cm to those 20 cm tall (Hayakawa, Thorhallsdottir, 1994). Lactation, which increases energy 1991) and preferred seminatural herbage in lawns less than demands of mares, might be expected to increase foraging 4 cm high (Fleurance et al., 2001), Naujeck et al., (2005) re- durations, yet studies showed that lactating mares were sim- ported that horses preferred perennial ryegrass swards 15 cm ilar to other pastured horses, spending about 61â70 percent high to those less than 4.5 cm. Grass, 6.6â9.4 cm in height, of their time feeding (Crowell-Davis et al., 1985; Duncan, was equally well eaten (1.5â1.7 kg DM/100 kg body weight 1985). As pasture availability increased, there was a linear [BW]) by yearling and 2-year-old horses, although 2-year- decrease in time spent grazing (Arnold, 1984). With grass old horses ate more forage per bite (9.9 vs. 7.6 g organic senescence, horses decreased both pasture intakes (1.8â2 kg matter [OM]) and spent less time foraging (59 percent vs. 66 DM/100 kg BW) and grazing time (52â58 percent of the percent of the day) than yearlings (Mesochina et al., 1998). day) (Shingu et al., 2000). Voluntary intakes of fresh forages Nonpregnant draft mares pastured on wet grasslands con- by various classes of equids are summarized in Chapter 8 sumed 166.2 g OM/kg W0.75, an intake of about 3.3 kg/100 (Table 8.1). Daily pasture intakes ranged from 15â32 g DM/ kg BW (Fleurance et al., 2001). In addition, forage selection kg BW (average 20 g DM/kg BW). and intake may be dictated by seasonal sward growth. In Horses are constant feeders. When grazing, horses take a spring, horses moved to areas where the first pasture grew bite of grass, then move forward one or two steps, followed irrespective of its height or thickness (Salter and Hudson, by another bite (Feist and McCullough, 1976). Exmoor 1979). ponies walked 3â5 km daily in winter and 3.8â4.9 km in Such equivocal results suggest that fresh herbage intake summer (Booth, 1998). Similarly, Shingu et al. (2000) re- is governed by the interaction of a number of factors, in- ported that pastured horses moved a distance of 2.6â3 km cluding plant maturity/herbage quality and sward character- daily, of which 50â60 percent occurred during grazing. Con- istics, which dictate herbage bite mass, rather than sward sequently, horses eat and/or trample more pasture than cat- height per se. Indeed, Hughes and Gallagher (1993) found tle. Dry matter intake (144 g DM/kg W0.75) by horses on that herbage dry matter (DM) intakes by horses did not pasture was 63 percent higher than by cattle (88 g DM/kg change with increasing sward height, for although herbage W0.75) (Menard et al., 2002). The time spent grazing by non- bite mass increased, bite rate decreased, maintaining con- pregnant horses (47 percent of the day or 11 hours) was stant intakes. Quality and quantity of vegetation in a grazing longer than by cattle (32 percent) or sheep (37.5 percent) area affect grazing rate and time spent grazing. Time budget sharing the same pastures (Arnold, 1984). Menard et al. experiments have shown that horses at pasture generally (2002) observed that breeding mares spent 54 percent of the graze for 10â17 hours daily (Martin-Rosset et al., 1978; day grazing in summer compared to cattle, which grazed for Crowell-Davis et al., 1985; Gallagher and McMenniman, 36 percent of the day. Autumnal grazing time increased to 1989; Duncan, 1992; Fleurance et al., 2001). Hughes and 68 percent for mares and 45 percent for cattle, suggesting a Gallagher (1993) and Gallagher and McMeniman (1989), sparser pasture supply. Although horses graze or eat for studying horses pastured on warm-season species and longer periods than ruminants, if time spent ruminating is perennial ryegrass, respectively, concluded that horses added to active foraging by cattle, the time budgets of both needed to graze for approximately 17 hours daily to meet species is very similar. their nutritional needs. Gender, age, and breed all influenced The range of DM intakes of selected feeds by horses, time spent grazing. Thus, stallions grazed for lesser periods ponies, and donkeys is given in Table 11-1. Mature and than mares, weanlings less than mature horses (Crowell- young horses appear to have a maximal daily DM feed in- Davis et al., 1985), and 2-year-olds less than yearlings take of about 3â3.2 percent of their body weight, although (Mesochina et al., 2000). Furthermore, single animals average intakes appear to be lower. Ponies may have higher grazed for shorter periods than when in a herd (Kusonose et voluntary dry matter intake (VDMI) than horses. Ponies ate al., 1986) and Arabians grazed for longer periods than Thor- 3.9 kg/100 kg BW alfalfa hay (Pearson et al., 2001) and up oughbreds (Rogalski, 1977). Nocturnal intakes may account to 5.1 kg fresh weight/100 kg BW of 60 percent hayâ40 per- for between 20â50 percent of the total time spent grazing cent concentrate pellets (Argo et al., 2002). In the latter (Doreau et al., 1980; Fleurance et al., 2001), but this is also study, the feed intakes seem atypically high, but these ob-
214 NUTRIENT REQUIREMENTS OF HORSES TABLE 11-1 Summary of Ranges of Reported Average Voluntary Dry Matter Intakes (AVDMI) of Selected Feedstuffs Ranges of AVDMI (kg/100 kg Classification BW/d) References Mature horses 1.8â3.2 Aiken et al. (1989); Crozier et al. (1997); Fresh forage, all hay, mixed concentrate and hay Dulphy et al. (1997a); Dulphy et al. (1997b); and complete, processed mix diets Heusner (1993); Marlow et al. (1983) Mature ponies 1.5â5.2 Argo et al. (2002); Bergero et al. (2002); Hale Hay and complete, processed mix diets and Moore-Colyer (2001); Moore-Colyer and Longland (2000); Pearson and Merritt (1991); Pearson et al. (2001) Mature ponies 1.5â2.4 Pearson and Merritt (1991); Pearson et al. Straw diets (2001) Growing horses 2.0â3.0 Aiken et al. (1989); Cymbaluk et al. (1989); Fresh forage, all hay and mixed concentrateâ Guay et al. (2002); LaCasha et al. (1999); hay diets McMeniman (2000) Donkeys 2.3â2.6 Pearson et al. (2001) Alfalfa hay Donkeys 0.8â1.6 Pearson and Merritt (1991); Pearson et al. Oat-straw diet (2001) servations might not be unexpected after a period of feed re- the time taken to eat 0.5 g or 1 g grain/kg BW was consid- striction or when the feed is exceptionally palatable. Typical erably shorter at 176 and 281 seconds, respectively. The av- voluntary intakes of various hays by mature horses were re- erage time taken by mature horses to eat 1 kg of dry hay, ported at about 2 kg DM/100 kg BW (Dulphy et al., 1997a) moist hay, whole oats, barley, and corn was 36.5, 29.7, 9.3, and were remarkably similar despite differences in hay nu- 9.1, and 13.8 minutes, respectively (Bergero and Nardi, trient composition (Martin-Rosset and Dulphy, 1987; Dul- 1996). Crushed or pelleted grains took less time to consume phy et al., 1997b). Ad libitum-fed legume and grass hays than whole, dry grains. containing 52 percent and 66 percent neutral detergent fiber Meal size and frequency for horses are affected by diet (NDF), respectively, were consumed at the rate of 2â2.4 kg type. Ponies ate a 60 percent grass hayâ40 percent concen- DM/100 kg BW by both young and mature horses (Martin- trate pellet more often (30 meals/d) than the same diet fed as Rosset and Dulphy, 1987; Dulphy et al., 1997b). The excep- chaff (23.8 meals/d) (Argo et al., 2002). Geldings ate 8.4â13 tions were barley straw, whose VDMI by horses was 0.9 kg meals daily consuming 52â1,179 g/meal when fed alfalfa DM/100 kg BW (Dulphy et al., 1997a); oat straw, whose hay, grass hays, or barley straw (Dulphy et al., 1997a). VDMI by ponies was 2.4 kg DM/100 kg BW (Pearson et al., Horses spent an average daily time grazing either a wood- 2001); and corn silage, which was eaten at the rate of 0.97 land or summer pasture of 938 and 980 minutes, respec- kg/100 kg BW (Martin-Rosset and Dulphy, 1987). The low tively, compared to only 856 minutes eating hay when kept intake of straw by ponies compared to that of alfalfa hay was in a drylot (Kondo et al., 1993). attributed to an increased mean gastrointestinal particle re- The form and composition of the diet and age of the tention time (Pearson et al., 2001). horse affect bite size, bites/minute, and chews/bite. The re- Meal length on pasture by feral horses ranged from a few lationship between diet type and various eating criteria are minutes to 13.5 hours (Mayes and Duncan, 1986). The aver- given in Table 11-2. Ponies fed a pellet comprised of 60 age duration of all hay or straw meals by light horse geldings percent chopped forage (voluntary feed intake [VFI] of 5.1 ranged from 151â188 min/meal (Dulphy et al., 1997a) and kg fresh weight/100 kg BW) ate the pellet 54 percent more was considerably longer than the 21â30.6 minutes that pony rapidly than the same diet offered as chaff (Argo et al., mares needed to consume a meal of 60 percent hayâ40 per- 2002). A similar amount of diet was consumed per bite cent concentrate chaff or pellets (Argo et al., 2002). The time (about 5 g DM/bite), but the number of bites was signifi- taken to consume 0.5 g hay/kg BW was 617 seconds; dou- cantly greater for pellets (5.2 bites/min) than chaff (3.8 bling the feeding rate to 1 g/kg BW increased feeding time bites/min). However, eating chaff required more chews per to 1,065 seconds (Lorenzo-Figueras et al., 2002), whereas bite (22.8/min) than pellets (16.1/min), with the result that
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 215 TABLE 11-2 Foraging Criteria by Horses Provided Various Feeds Bite or Chew DM Intake Frequency DM Intake Feed Type (kg/100 kg BW) (bites/min) (g/min) Reference 60% forage pellet Variable, maximum 4.5 5.2 26.2 Argo et al. (2002) 60% chaff pellet Variable, up to 2.2 3.8 17 Argo et al. (2002) Legume hay 2â2.35 12.6â14.2 Dulphy et al. (1997a) Grass hay 2â2.43 12.3â14.4 Dulphy et al. (1997a) Grass hay 4.7â5.5 4.6â5.2 Shingu et al. (2001) Barley straw 0.91â1.0 7.6â7.9 Dulphy et al. (1997a) Orchardgrass pasture 11â12 10â12. 4 Duren et al. (1989) Mixed grass pasture 1.54â1.71 7.6â9.9 Mesochina et al. (2000) Endophyte pasture 16â18 Pfister et al. (2003) Alfalfa pasture 8 Pfister et al. (2003) Fresh alfalfa 15 40.4 Gross et al. (1993) Kentucky bluegrass 30.3â54.1 Kawai et al. (2004b) Native grass hay and concentrate Pregnant 1.88 10.2 Lactating 3.13 15.2 Boulot et al. (1987) Pellet (50%)âalfalfa chaff (15%)âbeet pulp (35%) 77 Â± 12.8 147 Â± 36.8 Ellis et al. (2005) Pellet only as above 65 Â± 11.6 140 Â± 19.4 Ellis et al. (2005) Trial pellet (TP; 80%)âmolasses (10%)â short chopped alfalfa (10%) 69 Â± 9.3 161 Â± 32.1 Ellis et al. (2005) TP + 10% chopped 68 Â± 9.2 to 94 Â± 15.7 Ellis et al. (2005) straw 2.5 or 4 cm 71 Â± 8.6 99 Â± 19.4 TP + 20% chopped 66â68 Â± 10 75 Â± 13.1 Ellis et al. (2005) straw 2.5 or 4 cm 77 Â± 15.6 TP + 30% chopped 68 Â± 9.1 64 Â± 15.2 Ellis et al. (2005) straw 2.5 or 4 cm 69 Â± 9.7 66 Â± 15.4 less chaff DM was eaten per minute (17 g DM) than pellets concentrate diet compared to 10.2 g/min by pregnant mares (26.2 g DM). The applicability of using short chaff (< 2 cm) (Boulot et al., 1987), likely reflective of the higher energy to slow sweet-feed intake was examined by Harris et al. demands imposed by lactation. These authors observed that (2005) who found that the addition of 35 percent chaff to a lactating mares spent 1,087 Â± 105 min/d eating compared to sweet-feed meal effectively doubled the time to consume the pregnant mares, which spent 944 Â± 195 min/d eating. Horses meal, but it also increased the minute intake rate, which may overwintered in paddocks consumed hay at the rate of be undesirable. 4.6â5.2 g DM/bite (Shingu et al., 2001). Bites occurred at Bite size and maximal intake rates (g DM/min) increase the rate of 4.7â5.5 /min with a chewing rate of 64â68. The in proportion to body mass, but grazing rate (min/bite) has addition of chopped straw either of 2.5 or 4 cm in length at similarity irrespective of animal species (Gross et al., 1993). rates of 10, 20, and 30 percent to a pelleted diet mixed with Diet affects bite size and minute intake rates in horses chopped alfalfa produced no effect on chews/min, increased (Duren et al., 1989; Gross et al., 1993; Dulphy et al., 1997a; (P < 0.001) time taken to consume 1 kg wet matter and de- Shingu et al., 2001; Pfister et al., 2002; Kawai et al., 2004b). creased intake rates, but not significantly (Ellis et al., 2005). Geldings ate about 12.2â14.3 g DM grass or alfalfa hay/min Widely divergent minute intake rates are evident for but only 7.6 g DM barley straw/min (Dulphy et al., 1997a). green forage (Table 11-2), which may reflect differences in Horses fed straw spent less time eating daily (559â605 methodology. Forage biting rates by exercised and nonexer- min/d) than horses fed hay (748â852 min/d). Consequently, cised yearling horses grazing orchardgrass were 11â12/min total intake of barley straw was significantly lower than with a DM intake rate of 0.86 g/bite and a minute intake rate for hay. Lactating mares consumed 15.2 g/min of a hay- of about 10 g/min (Duren et al., 1989). Forage biting rates
216 NUTRIENT REQUIREMENTS OF HORSES decreased over the allotted 3-hour grazing period. Con- ing and/or kicking aggression (Keiper and Receveur, 1992; versely, Kawai et al. (2004b) observed a much higher bite Sigurjonsdottir et al., 2003; Pluhacek et al., 2006). Horses frequency and lower chew rates. Biting rate increased from grazed, ate hay, and rested with preferred individuals when 30.3 to 54.1 bites/min as sward height of a Kentucky blue- competition for feed was unlimited, but aggressive interac- grass pasture decreased with a concomitant reduction in tion by horses became evident when feed was limited chewing rate from 84.5 to 66.5 times/min. The chewing rate (Arnold and Grassia, 1982; Wood-Gush and Galbraith, of fresh alfalfa was similar (91 chews/min) (Gross et al., 1987). Pregnant and barren mares typically had at least one 1993). Horses grazing endophyte-infected forage had more partner whose close proximity was tolerated over other bites/min (16â18) than horses grazing alfalfa (8 bites/ min) horses, whereas mares with foals diverted their social at- (Pfister et al., 2002), which suggests horses do not have the tachment to their offspring (Estep et al., 1993; van Dieren- innate ability to discriminate forages that might be poten- donck et al., 2004). Kinship and familiarity have a signifi- tially harmful. cant impact on partner preference and dominance within a herd (Keiper and Sambraus, 1986). Consequently, related horses or horses that have resided together will likely toler- Animal Factors Affecting Feed Intake ate closer proximity to each other within the feeding area. Young horses appear to eat more per unit BW than ma- Hierarchy among horses has been documented (Ellard and ture horses (Table 11-1), but feed intake comparisons be- Crowell-Davis, 1989; Boyd, 1991), so vigilant oversight of tween young and mature horses may be misleading unless group dynamics is necessary to avoid malnutrition or obe- both groups are fed similar diets. Boyd (1988) confirmed sity as a result of submissiveness and dominance in the that foals from the age of 5 months to the age of 14 months group structure. Holmes et al. (1987) observed that subordi- spent more time in feeding activity than mature horses. nate horses had an extended latency period (> 200 sec) when However, the age-feed intake response of Danish Warm- eating in close proximity to dominant pen-mates. This be- blood weanlings fed a total mixed ration (TMR) varied with havioral situation was solved by providing a wire partition energy content of the diet (Sondergaard, 2003). Feed intake on the feeders, which allowed subordinate horses to eat of a TMR containing about 1.24 Mcal net energy (NE)/kg while continuously observing their dominant pen-mates. DM decreased from about 2 kg/100 kg BW by 5-month-old However, isolation of subordinate horses in competitive foals to 1.7 kg/100 kg DM when the foals were 1 year of feeding situations may be contraindicated because horses age. By comparison, 5-month-old foals fed a TMR contain- appear to be stimulated to eat by visual contact of compan- ing 1.04 Mcal NE/kg DM ate about 1.5 kg DM/100 kg BW, ion horses. Visibility of other horses, particularly in the af- which increased to about 2 kg DM/100 kg BW by 1 year of ternoon, reportedly increased the time spent feeding by pony age. From 16.5 months through 24 months, feed intake de- mares (Sweeting et al., 1985). Houpt and Houpt (1988) con- creased from about 2 to 1.8 kg/100 kg BW irrespective of firmed that horses isolated from direct visual contact of oth- diet caloric content. ers were three times more active and spent 51.5 percent less Forage eating rates may be breed-related. Hokkaido time eating compared to being housed together or separately native horses consumed a similar amount of feed (1.5 kg but in visual contact of other horses. DM/100 kg BW) over a shorter period of time (6.7 hours) Growing horses, exercising horses, pregnant mares, lac- than cross-bred light horses (9.3 hours) (Shingu et al., tating mares, and stallions during the breeding season re- 2001). Light pregnant mares maintained in straight stalls quire more nutrients than horses at maintenance. Heavy or spent significantly more time eating (57.9 percent of the draft horses require more total feed than light horses by day) than similarly housed draft mares (50.2 percent) (Flan- virtue of body weight. Lactation increased the voluntary for- nigan and Stookey, 2001). Yet, the voluntary DM intake of age intake by 65 percent compared to the same mares dur- 90 percent hayâ10 percent concentrate by pregnant light and ing pregnancy (Boulot et al., 1987). Feeding strategies should heavy mares was similar at 1.73 and 1.82 kg/100 kg BW, re- consider these differences, and farm facilities should sepa- spectively (Doreau et al., 1991). rate group-housed horses into different production classes. Feeding activity was marginally increased immediately Use of individual feeding containers may help some horses after strenuous exercise, whereas time spent drinking water to consume allotted amounts in group-fed situations. Dis- increased markedly (Caanitz et al., 1991). However, exercise tance between feeding containers should be determined by had no long-term impact on time spent eating. observing each groupâs eating behaviors. Likewise, size of Regulating feed intake in grouped, meal-fed horses pre- the group-fed herd may need to be reduced to decrease horse sents unique challenges. Herd social orders, as well as vari- density in the eating area and to reduce the time required to ation in appetites and intake rate of individual horses, can deliver the portions to every feeding container. Horses re- cause differences between amounts allotted and amounts ac- quiring significantly less or more time than the herdâs aver- tually consumed. Age along with residency time in the herd age to consume feeds may need to be fed separately. have been identified as the main factors in the social rank of Confinement can aggravate dominance behavior in wild equids and Icelandic horses and was established by bit- horses. Przewalskiâs horses kept in a small pen showed a
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 217 46â76 percent increase in aggressive behavior (threats, combination of this added work to get feed and the poor nu- bites, and kicks) compared to horses housed in large pad- tritional quality of the feed under snow underscores the need docks (Hogan et al., 1988). Young or timid horses may be to monitor horses daily on winter pastures and to provide driven away from feed if inadequate feeding space is given. supplementary hay (and perhaps grain) when needed (see However, spacing feeders at distances ranging from 2.4â9.7 Chapter 12, Feeding Management of Horses in Cold or Hot meters had less effect than the arrangement of the feeders Weather). (Janicki et al., 1999). Placing feeders in a triangle appeared Horses graze in a diurnal pattern with an early morning to improve the feeding opportunities of submissive horses. and dusk component (Salter and Hudson, 1979; Duncan et Dominance behavior should be considered whenever de- al., 1984; Crowell-Davis et al., 1985; Berger et al., 1999). signing feeding arrangements for two or more horses that Peak feeding by pastured Welsh ponies occurred between will be kept in a confined area. To avoid competitive prob- 5:00 to 9:00 am then again at dusk from 5:00 to 9:00 pm lems among group-fed horses, it may be necessary to in- (Crowell-Davis et al., 1985). Natural patterns of feeding are crease the availability of feed and/or to increase the feeding modified in modern husbandry systems of confinement and area. Timid animals may need to be fed separately but in vi- restricted feed access. Horses kept in a drylot and fed or- sual contact of other horses to ensure that sufficient feed is chardgrass hay spent 90 percent more time lying down ingested to maintain a satisfactory body weight. (63 min/d vs. 33 min/d) and spent 8â12 percent less time Fever, anorexia, and depression are common signs of ill- feeding than horses grazing similar pastures (Kondo et al., ness in all animals (Hart, 1988). The most common recog- 1993). nizable clinical symptom of illness in horses is inappetence. Seasonal changes in ambient temperature and day length Sick horses eat little or do not eat at all. Usually, horses that altered the absolute ultradian and daily patterns (Berger et reduce their feed intake will also reduce their water intake al., 1999). In French wetland pastures, grazing by barren (see Chapter 7). Dental and head pain have specific behav- mares occurred principally (74 percent) at night (Fleurance ioral indicators, including altered eating patterns, anorexia, et al., 2001) and grazing time was generally greatest in feed refusal, quidding, and food pocketing that may con- spring and autumn (Rogalski, 1975). Fleurance et al. (2001) tribute to weight loss (Ashley et al., 2005). reported horses spent 12 and 16 hours grazing in summer and autumn respectively, while Kaseda (1983) found that horses grazed less in winter than summer. During warm Environmental Effects on Feed Intake weather in summer, horses increased the time spent standing Grazing time can be affected by environmental condi- (Berger, 1977; Booth, 1998). Lactating pony mares reduced tions. High rainfall and high winds resulted in decreased feeding activity in summer, typically spending more time time spent grazing (Rogalski, 1975) as did high tempera- resting in the shade during late mornings and afternoons tures, but increased relative humidity increased grazing time (Crowell-Davis et al., 1985). Camargue and Przewalskiâs (Rogalski, 1974). Horses spent more time feeding during horses rested during peak heat periods of the day, and any cold weather and less during hot weather (Booth, 1998). grazing during the heat of the day was considered atypical Horses grazing on pastures during a Scottish winter had a and was concluded to be an indicator of undernourishment higher bite rate (61.4 vs. 52.4/min), step rate (6.7 vs. 4.2 (Mayes and Duncan, 1986; Klimov, 1988). Rainfall did not steps/min), and step distance (0.058 vs. 0.021 m/step), but significantly affect foraging by Camargue horses, but horses fewer bites/step (10 vs. 12) than in summer (Booth, 1998). spent more time in standing rest and less time lying down Snowfall at sub-zero temperatures typically did not disrupt (Duncan, 1985). feeding if supplementary feed was available, but shelter- Infestations of mosquitoes, ticks, horseflies, and other seeking behavior occurred when cold weather was coupled external parasites disrupt feeding activities of horses. Horses with wind (Booth, 1998). Where winter grazing is practiced, reduced the length of feeding bouts when biting flies were the impact of snow on feed intake is related to the depth active (Mayes and Duncan, 1986) and shifted feeding activ- of the snow cover. Horses grazing on pastures with 20 cm ities to periods of the day when lower ambient temperature of snow reduced daily grazing time to 416 min/d and re- reduced irritating insects (Duncan, 1985). Insect activity duced DM intake to 2.1 kg/100 kg BW compared to the 544 was positively related to ambient temperature but decreased min/d spent grazing on nonsnowy pastures and intakes of with wind speed (Keiper and Berger, 1982). During periods 2.7 kg/100 kg BW on nonsnowy pasture (Kawai et al., of high fly activity (typically from 10:00 am to 4:00 pm), 2004a). The decreased DE intake created by snow on pas- Assateague ponies spent time on beaches or dunes and re- tures resulted in weight loss of the horses. Horses generally duced feeding activity by 11â16 percent compared to other seek out areas with less snow cover because deep snow periods of the day (Keiper and Berger, 1982). By compari- (40â50 cm) required 10 times the activity in pawing (âcra- son, feral horses in mountainous areas moved to higher ele- teringâ) compared to that needed to uncover grass with a vations and stood in snow patches to avoid flies. Booth light snow cover (10 cm) (Salter and Hudson, 1979). Paw- (1998) reported that Exmoor ponies preferred to stand on ing through snow cover for feed has a high energy cost. The bare ground when Tabanids (horse flies) were active, which
218 NUTRIENT REQUIREMENTS OF HORSES reduced their time spent grazing. The nuisance effect of sucrose to oats increased the quantity of oats eaten by ponies flies, ticks, and lice on feeding behavior of horses, and as- compared to plain oats, as did the addition of 2.5 percent sociated weight loss, can result in large economic costs as- molasses for four of five ponies (Hintz, 1980; Hawkes et al., sociated with unthriftiness, reproductive failure, and disease 1985). The authors reported that 67 percent of the test (Steelman, 1976). Insect annoyance should always be con- ponies preferred oats with 10 percent sucrose compared to sidered as a potential cause of weight loss when pasture plain oats or oats with 2 percent sucrose. Horses also pre- quality is not a contributing cause. ferred the taste of sugar solutions to plain water (Randall et al., 1978). Sidedness or handedness, i.e., preference for eat- ing grain from the left or right hand side of the manger, was Feed Effects on Feeding Behavior observed in one of six ponies (Hintz, 1980) and has been Orosensory sensations are equated to palatability, which confirmed by others (Bottom et al., 2004), who found that has been defined as the smell, texture, and taste characteris- older horses had a stronger side preference than younger tics of a feed that determines its rate of intake (Dulphy et al., horses. 1997a). Coarseness and brittleness are examples of textures Hawkes et al. (1985) also tested the preferences of other that can negatively affect hay intake by horses. Textures can feed ingredients and their threshold acceptability. A basal be altered by feed processing, which can lead to very differ- mixed feed was preferred to the same feed to which 20 ent feed intakes (Haelein et al., 1966; Hintz et al., 1985). Fla- percent blood meal, meat and bone meal, or beet pulp were vorings and sweeteners have been used to increase feed in- added, whereas 20 percent alfalfa meal and 5 or 10 percent take by horses (Goodwin et al., 2005b). The impact of meat and bone meal additions were equally palatable to the physical forms of feed, criteria of feed quality, and chemical/ ponies as the basal mix. physical properties of grasses, hays, and pastures on feed in- Ponies preferred a basal mixed feed with 20 percent take are discussed elsewhere in this publication (Chapters 8 added dry distillersâ grains over the basal diet (Hawkes et al., and 14). 1985), yet the substitution of dry wheat distillersâ grain for a As indicated above, horses prefer certain pastures, hays, cereal-based concentrate in increments of 25 percent re- and grains, but they also appear to like variety in their diet duced intake and the rate of ingestion by horses in a near lin- as evidenced by the wide range of forages consumed by ear fashion (Hill, 2002). Intakes were based on access of feral horses (Salter and Hudson, 1979). Feeding preferences horses to 1-kg concentrate mixture over 10 minutes and, exist for forages and roughages (Archer, 1978a; Carson and thus, this study did not evaluate whether the horses would Wood-Gush, 1983). Although constant feeding of the same consume the mix over an extended period. Nevertheless, ac- diet may help reduce digestive problems (Lewis, 1995), it ceptance of the distillersâ grain did not appear to occur over may also lead to long-term monotony, which may lower feed time. Soaking the concentrate with water lowered palatabil- intake and contribute to abnormal stall behaviors (Mc- ity of the basal concentrate, which was further reduced when Greevy et al., 1995a). Long-term monotony may have distillersâ grains were added, thus resulting in a lowered feed caused stall-housed horses to reject hay they had previously intake (Hill, 2002). preferred in favor of other roughage choices (Goodwin et Fats have been added to horse diets to increase energy al., 2002; Thorne et al., 2005). In these studies, horses pro- supply and added in smaller amounts to reduce feed dusti- vided with an array of forage choices reduced their bedding ness. At the concentrations needed to influence energy in- intake, and increased the time and frequency of foraging take, flavor of oil/fat may influence feed intake. Horses fed activity. diets to which various oils and fats had been added preferred Horses become accustomed to the tastes and textures of diets containing only added corn oil (Holland et al., 1998). feeds to which they are exposed during growth, i.e., a Diets to which peanut, safflower, cottonseed, or mixtures of learned behavior. Horses born and raised in upstate New either corn oil, soy, or corn lecithin were added to either York preferred oats over corn and corn over barley (Hawkes corn or soy oil, various animal-vegetable oil blends, fancy et al., 1985), but in western Canada, where horses are rarely bleached tallow, hydrolyzed tallow flakes, or inedible tallow exposed to whole or cracked corn, oats were the most pre- were eaten less well. Horses rejected inedible tallow and ferred grain but barley was preferred over corn (Cymbaluk, fancy bleached tallow diets. Horses fed diets containing 10 1983). For this reason, horses that have been recently moved percent corn oil, corn oilâsoy lecithin, or soy lecithinâsoy to a new region may reject local feeds. Knowing the types oil consumed all of the diets well and showed reduced reac- and preferences of feeds the horse received at its previous tivity to a startle test compared to horses fed a control diet stable and supplying similar feeds can help ease the transi- of chopped hayâconcentrate (Holland et al., 1996). tion of the horse to its new environment. Horses may need a Flavorings and additives are occasionally used to mask period of adaptation before they accept novel feeds. unpalatable ingredients or to enhance intake of livestock Sucrose and other sweeteners and flavorings are added to feeds (Kunkle et al., 1997). Garlic, an additive in pet diets, improve intake of feed by horses by taste alone or to mask increased the concentrate intake by horses when added at distasteful feeds. Adding even small amounts (2 percent) of the rate of 1.5â3 g/kg (Horton et al., 1990). Garlic appar-
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 219 ently has moderate palatability to horses but has been con- (1 kg/d) contaminated with 14 Âµg/kg deoxynivalenol, 0.7 sumed in amounts causing toxicosis (Pearson et al., 2005). Âµg/kg 15-acetyldeoxynivalenol, 6.4 Âµg/kg fusaric acid, and These authors reported that horses that voluntarily ate more 2 Âµg/kg zearalenone compared to horses fed uncontami- than 0.25 g/kg BW freeze-dried garlic twice daily devel- nated grain (2.8 kg/d) (Raymond et al., 2003). Intake of the oped Heinz body anemia. The amounts of garlic typically contaminated feed did not increase over a period of 3 weeks added to concentrate mixtures are considerably below this so adaptation did not occur. Continued reluctance to eat any amount. feed should always be investigated. Preference and foraging studies in which horses were of- Aversion learning, however, is limited in horses. With a fered four low-energy concentrate mixes showed that horses few exceptions, horses given lithium-chloride by stomach- would eat some feed from each container, but tended to eat tube, which causes nausea, could be taught to avoid eating more of a high-fiber concentrate than mixes with a lower locoweed under hay-fed and grazing conditions (Pfister et fiber content (Goodwin et al., 2005a). Adding flavors and al., 2002). However, horses grazing early pastures contami- sweeteners to the diet altered concentrate preferences. nated with spotted locoweed were unable to discriminate be- Horses provided with an array of concentrates ate more tween nontoxic plants and locoweed (Pfister et al., 2003). In often, had shorter eating bouts, and collectively ate longer fact, horses ate more bites of locoweed (toxic component, each day than those offered only one concentrate. The cor- swainsone) than cattle, resulting in high serum swainsone rect combination of garlic, flavorings, and sweeteners ap- concentrations and, ultimately, depression and anorexia, peared key to whether horses rejected or preferred a diet signs indicative of clinical swainsone toxicity (Pfister et al., (Goodwin et al., 2005a). In some combinations, horses ate 2003). Although horses are selective grazers, they differ in more of the seasoned feed; other combinations were less their ability to discriminate between normal and toxic weeds popular. Mint-flavored diets were preferred over garlic- (Marinier and Alexander, 1992). Pony mares fed pelleted ra- flavored diets when added to pelleted grain with the same tions comprised of 45 to 60 percent perennial ryegrass con- energy content (Cairns et al., 2002). However, when the en- taminated with Penicillium cyclopium continued to eat the ergy content of the pellet was varied, the high-energy diets, diet despite development of neurological signs of ryegrass which contained 20 percent more dietary energy than the staggers (Blythe and Holtan, 1983). Therefore, innate intel- low-energy pellets, were preferred irrespective of flavor ligence should not be relied on to prevent ingestion of toxic added. Under the conditions of the study, the associated hay plants or contaminated diets. was high quality. Whether the preferences would hold true if Adult horses appear to have an aversion to eating grass low-quality hay had been provided was not examined. that has been contaminated by equine feces (Odberg and In a subsequent study, Goodwin et al. (2005b) examined Francis-Smith, 1977). Horses restricted to pastures may per- the effect of 15 flavorings on consumption of 100 g of ce- form âlatrineâ behavior whereby they graze and defecate in real byproduct. These authors found that the flavored separate areas. This behavior produces a pasture containing byproduct was eaten well in most cases and that prefer- âroughs and lawns,â in which the âlawnâ areas are preferen- ences of the top eight flavorings were fenugreek > banana tially grazed and the toilet areas are comparatively lightly > cherry > rosemary > cumin > carrot > peppermint > grazed, leading to rank overgrowth of pasture (Odberg and oregano. When the consumption rate of unflavored mineral Francis-Smith, 1976). However, horses accepted grass cut pellets was compared to banana- and fenugreek-flavored from roughs as long as no feces were present, indicating an pellets, the flavored pellets were eaten at rates 3 to 3.75 aversion to feces rather than the herbage in roughs per se times more rapidly. This supports the observation that (Odberg and Francis-Smith, 1977). Horses have been re- horses accept variety in their diet. Although these data sug- ported to reject pastures where feces have contacted the grass gest that flavorings stimulate intake of certain feeds by for longer than 24 hours (Archer, 1978b), despite the greater horses, flavorings should be added judiciously. Horses canopy growth in latrine areas compared to those in noncon- naÃ¯ve to certain feed flavors and textures may require grad- taminated areas (Loucougaray et al., 2004). ual exposure to a flavored diet. It has been suggested that such a grazing pattern reduces the parasite load to the grazed areas by spatial separation of feeding and defecating areas (Taylor, 1954). However, Fleu- Feed Contaminants and Taste Aversions rance et al. (2001) proposed that this behavior resulted in a Taste aversion of feeds is a learned behavior, occurring constantly producing vegetative regrowth with greater nutri- when horses become sick immediately after feed is con- tional value in the grazed area than that of more mature un- sumed but not if illness is delayed (Houpt et al., 1990). grazed forage in the rough latrine areas. However, with time, Horses exposed to feed contaminated with monensin, an some nutrients, particularly potassium and phosphorous, ionophore toxic to horses, became anorexic or ate the diet may become deficient in lawns through their gradual trans- reluctantly after an initial exposure (Matsuoka et al., 1996). fer to the roughs in the feces (Archer, 1973; Odberg and Similarly, horses reduced their intakes of mycotoxin- Francis-Smith, 1977). Truly free-ranging horses, however, contaminated feed. Horses ate about one-third of a grain mix may not have latrine behavior and tend to defecate where
220 NUTRIENT REQUIREMENTS OF HORSES they graze (Lamoot et al., 2004). Defecations and urinations ing salt (Salter and Hudson, 1979), although this has not by mares in a grazing area were positively correlated to been further studied. In domesticated horses, geophagia oc- grazing time. That is, if horses grazed in an area for a long curred in clinically normal horses that had access to mineral time, they also soiled the area more often. In grazed pas- mixes (54 percent) and/or access to supplementary feed (71 tures, latrine areas can occupy from 30 percent of wetland percent) (McGreevy et al., 2001). Soil iron and copper in pastures to 89 percent of flatland pastures (Loucougaray et licked soils were higher, but the mineral concentration al., 2004). Thus, horses have no conception that they are among and between licked and unlicked soils was so widely contaminating the pasture they will have to eat. Therefore, variable that it suggests that geophagia may not be a simple efficient management of small pastures may require removal pursuit for trace minerals. or harrowing of feces on a regular basis to prevent rejection Although dirt-eating is generally innocuous, consump- of the pasture. tion of sandy soil can cause colic or diarrhea (Bertone et al., 1988; Husted et al., 2005). Sand-eating has been estimated to cause up to 30 percent of colic cases, particularly in re- UNUSUAL ORAL BEHAVIOR gions with sandy soils such as the southern United States (Lieb and Weise, 1999). These authors found that feeding Coprophagy, Geophagia, and Wood-Chewing concentrate on sand resulted in inadvertent sand consump- Unusual oral behaviors include coprophagy, geophagia, tion by horses, whereas feeding hay on sand resulted in lit- and wood-chewing that are not defined as stereotypic be- tle to no sand intake. Subsequently, Weise and Lieb (2001) haviors because they appear to represent a normal physio- evaluated the effect of feeding a low-protein diet (70 percent logical or foraging response (Francis-Smith and Wood- of basal requirements), a low-energy diet (75 percent of Gush, 1977; Salter and Hudson, 1979; Crowell-Davis and basal requirements), and a combination low energyâlow Houpt, 1985; Mills et al., 2005). Coprophagy, or feces eat- protein diet on sand intake. No differences were found in ing, is an apparently normal activity of foals as young as 5 sand intake when energy or protein intakes were below re- days of age extending to about 2 months of age (Francis- quirements. However, horse effects were highly significant Smith and Wood-Gush, 1977; Crowell-Davis and Houpt, (P < 0.001). That is, some horses were prone to eating sand, 1985). Typically, the foal consumes its damâs feces, but oc- whereas others were not. Although mineral intake also var- casionally the foal may eat its own feces or that of an unre- ied among horses, the amount of mineral consumed was un- lated adult. Under controlled, stall-housing conditions, co- related to sand intake. In a Danish study that evaluated sand prophagy occurred infrequently, once every 20.6 hours, intake by Icelandic horses, Husted et al. (2005) identified (Crowell-Davis and Caudle, 1989), but under grazing situa- both soil type and pasture quality as important variables in tions, eating of feces occurred on average every 4.3 hours sand-eating. Feeding horses off the ground when pastures for the first 2 months of age (Crowell-Davis and Houpt, were sparse or had no grass increased the probability of de- 1985). Thereafter, as the foal matured, the occurrence of tecting sand in the feces. The authors also noted a trend for feces-eating declined and was rarely seen by 6 months of thinner and younger horses to have detectable amounts of age (Crowell-Davis and Houpt, 1985). The purpose of co- sand in their feces. This study supported the recommenda- prophagy has been speculated to be a mechanism of popu- tion that horses kept in outdoor paddocks with sparse or lit- lating the neonatal gut with bacteria and protozoa (Crowell tle grass growth should only be fed from cribs or hay racks. Davis and Houpt, 1985), but an alternative hypothesis has Wood-chewing occurs in stabled and free-living horses in been proposed that foals eat feces to learn feed preferences which the horse gnaws on fencing, trees, or any similar (Marinier and Alexander, 1995). No nutrient motivation has wooden object and either discards or swallows bits of wood. been identified for feces consumption by foals, but mature Bark-eating has been reported to be not uncommon in feral horses that eat feces were suggested to lack sufficient feed, horses (Ashton, 2005), and about one-third of young Thor- fiber, or other nutrients (Feist and McCullough, 1976). The oughbreds chewed wood (Waters et al., 2002), which has led latter claims have been poorly researched, but several stud- to the assessment that this oral behavior may be a normal, ies have reported consumption of feces when alternative functional foraging behavior (Mills et al., 2005). Most often, feeds (whole corn plant, ryegrass straw) were fed either as wood-chewing has an economic rather than a clinical im- pellets, as cubes, or in long form at intakes below 1.3 kg/100 pact, but Nicol (1998) reported that wood-chewing appeared kg BW/d (Schurg et al., 1977; Schurg et al., 1978). Subnor- to precede cribbing in some horses and infrequently causes mal protein intakes existed in the latter study, which con- small intestinal obstruction due to wood splinters (Green founded the interpretation of which stimulus initiated the and Tong, 1988). coprophagy. Although the incidence of wood-chewing in foals was as Geophagia or dirt-eating is not uncommon in feral and high as 30 percent (Waters et al., 2002), pastured or stabled domesticated horses (Salter and Hudson, 1979; McGreevy horses wood-chewed only 5.1 and 8.1 percent, respectively et al., 2001; Weise and Lieb, 2001; Husted et al., 2005). In (Pell and McGreevy, 1999). The inciting causes of wood- feral horses, soil-licking was felt to be a method of acquir- chewing in horses are many and varied. Wood-chewing in-
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 221 creased during inclement weather (Jackson et al., 1985), feeds (Krzak et al., 1991). Weanlings confined to stables when diets were limit-fed, processed, or low in fiber content showed increased behavioral abnormalities such as cribbing, (Haelein et al., 1966; Krzak et al., 1991; Johnson et al., box-walking, and wood-chewing compared to weanlings 1998), during confinement (Krzak et al., 1991; Boyd, 1991), kept in paddocks (Waters et al., 2002). Use of a high-fat and and after weaning (Waters et al., 2002). High-concentrate high-fiber supplement at weaning appeared to relax the foals diets or pelleted feeds increased wood-chewing activity compared to those fed a high-sugar and high-starch concen- compared to horses fed long hay (Haelein et al., 1966; trate (Redgate et al., 2004). However, the durability of the Willard et al., 1977; Marsden, 1993; McGreevy et al., behavioral effect of a high-fat and high-fiber diet to prevent 1995a). High-starch (concentrate) intakes have also been wood-chewing has not yet been reported. The best predictor implicated in aggressive behavior when feeding horses, of wood-chewing has been reported to be roughage intake which was eliminated by feeding at least 1 kg hay/100 kg (Mills et al., 2005), which implies that to minimize wood- BW (Zeyner et al., 2004). Jackson et al. (1985) fed mature chewing, an adequate supply of roughage should be avail- Quarter horse mares either long alfalfa hay twice daily or able to the horse. cubed alfalfa hay two and three times per day at the rate of 2.5 kg/100 kg BW/d and found no difference in the amount Cribbing of wood chewed but noted a correlation of wood-chewing with inclement weather. During periods of cold, wet weather Stable vices or stereotypies are defined as apparently (â2.6Â°C and 39.8 cm rain), wood-chewing increased in the functionless, repetitive behaviors and include cribbing (crib- mares compared to periods of warm, dry weather (9.8Â°C and biting), weaving, and stall-walking (Nicol, 1998; Mills et 0.4 cm rain). al., 2005). Detailed descriptions of these conditions can be Horses fed long hay either ad libitum or in amounts to found in McGreevy (2004) and Mills et al. (2005). The inci- provide 100 percent of maintenance energy requirements dence of stereotypic behavior and factors associated in their spent 58â64 percent of their normal daily budget eating and occurrence were established in part by using research sur- showed few abnormal behaviors (0â2 percent) (Marsden, veys (Vecchiotti and Galanti, 1986; McGreevy et al., 1993). Feeding pelleted or processed feeds reduced the time 1995a,b; Luescher et al., 1998; Pell and McGreevy, 1999; spent eating to 10â12 percent of the day with a concurrent McBride and Long, 2001), which have led to some conflict- increase to 58â66 percent of time spent in abnormal behav- ing conclusions due to unavoidable confounding of data col- iors. Similarly, Houpt et al. (2004) reported that horses fed lected on horses located in different geographies, in various hay spent 50 percent of their daily time budget eating com- athletic or nonathletic disciplines, fed varying diets, and pared to only 10 percent when pellets were fed. Horses fed kept under a wide range of environmental conditions. Con- hay chewed 40,000 times per day compared to 10,000 times trolled studies have also produced conflicting outcomes, but per day for pellet-fed horses. In this study, motivation for the important contribution made by behavioral research has forage or pellets was tested when pellets were fed or when been the increased awareness of the complexity of stereo- hay was fed. The number of presses for pellets when hay typical and/or normal feeding behavior of horses. As a re- was fed had a median number of 25 compared to 12 presses sult, many of the interventions once used to arrest stereo- for hay when horses were fed the pelleted diet. These data typic behavior, such as punishment or physical prevention, suggest that horses are motivated for variety but also for for- have been recognized to be mostly ineffective and poten- age when pellets are fed, and for pellets when forage is fed. tially detrimental to the horseâs welfare, especially if no at- Feeding high amounts of concentrates or processed diets tempt has been made to resolve the instigating cause stimulates wood-chewing activity. Willard et al. (1977) ob- (Cooper and Mason, 1998; McGreevy and Nicol, 1998a,b; served a 5-fold increase in wood-chewing by concentrate- Nicol, 1998; McBride and Cuddeford, 2001; Mills et al., fed horses compared to hay-fed horses, which was accom- 2005). panied by a reduction in post-feeding cecal pH from 6.97 in Cribbing or crib-biting, stall-walking, and weaving are hay-fed horses to 6.64 in concentrate-fed horses. The wood- stereotypies that may have a breed, function, environmental, chewing activity may have been related to the decrease in feed management, age, or disease condition (Vecchiotti and cecal pH but may have also been a response to a low-fiber in- Galanti, 1986; Luescher et al., 1998; Bachman et al., 2003; take. Similarly, a dramatic increase was observed in wood- Archer et al., 2004; Nicol et al., 2005; Mills et al., 2005). chewing and eating of bedding after the diet was gradually Based on a survey of trainers, Vecchiotti and Galanti (1986) increased in grain over a 4-week period to account for 75 reported a 7.4 percent cribbing incidence in Thoroughbred percent of the total diet (Johnson et al., 1998). Wood- horses with a higher than usual prevalence in some families chewing occurred in 30 percent of weaned foals by 30 weeks that suggested a hereditary predisposition to cribbing. of age, and a higher incidence was observed in foals born to Luescher et al. (1998), using survey data obtained from dominant mares and confined to barns or stables at weaning pleasure horse and racehorse stables, found a cribbing inci- (Waters et al., 2002). Lack of exercise increased wood-chew- dence of 5.1â5.5 percent in pleasure and Thoroughbred ing several-fold in yearling horses fed principally pelleted horses but no reports of cribbing in Standardbred horses. A
222 NUTRIENT REQUIREMENTS OF HORSES similar incidence of cribbing (5.5 percent) was reported in low basal saliva production, and it has been postulated that young racehorses (McGreevy et al., 1995a) and in young the cribbing stimulated the production of saliva (Nicol, Thoroughbreds (10.5 percent) (Waters et al., 2002). The ath- 1998). McCall et al. (2001) confirmed the lower saliva pro- letic pursuits of dressage, eventing, and endurance created duction by cribbing horses compared to normal horses but risks of having abnormal oral or locomotory behaviors at a suggested that cribbing did not produce sufficient excess prevalence rate of 32.5, 30.8, and 19.5 percent, respectively saliva to effectively buffer the stomach or gastrointestinal (McGreevy et al., 1995b). The time spent in the stable, not tract acidity. Antacid therapy has been used to ameliorate the activity, contributed to the abnormal behavior. However, gastric acidity and cribbing in some horses (Nicol et al., the frequency of turnout or type of exercise did not affect 2002; Mills and Macleod, 2002), but this outcome may be cribbing occurrence in pleasure or racehorses (Luescher et inconstant. Garcia et al. (2005) found that antacid therapy al., 1998). Moreover, Marsden (1993) concluded that hous- reduced gastric acidity in cribbing horses, but had no effect ing method, whether pasture, box stalls, or tie stalls, had lit- on cribbing duration or frequency (Garcia et al., 2005). tle effect on eliciting abnormal behaviors, but that the form Overall, these studies suggest that high-concentrate diets of the diet clearly affected behavior. may contribute to cribbing in predisposed horses by creating Mares were less likely than stallions or geldings to crib, an acidic gastrointestinal tract. and risk of cribbing increased with age (Luescher et al., Feeding less than 6.8 kg forage/d and feeding hay rather 1998). However, wood-chewing and cribbing behaviors have than providing pasture increased the risk of wood-chewing been observed early in life, and 9.7 percent of preweaned and cribbing (McGreevy et al., 1995a). Feeding only one foals and 22.5 percent of post-weaned foals were reported to type of forage induced stereotypic behavior in horses that have these behaviors (Nicol and Badnell-Waters, 2005). showed no such behavior when fed a choice of hays (Thorne Post-weaned foals fed concentrate had a 4-fold increased et al., 2005). Feeding forage three times daily increased risk of becoming cribbers (Waters et al., 2002), and cribbing cribbing relative to feeding hay twice daily or feeding more foals had a higher incidence of gastric ulceration than non- often than three times per day (McGreevy et al., 1995a). cribbing foals (Nicol et al., 2002). Nicol and Badnell-Waters Bachman et al. (2003) identified a risk for cribbing associ- (2005) observed that foals that developed abnormal oral be- ated with feeding more than four times per day. Evidently, havior preweaning had more fragmented suckling intervals there are confounding factors that influence how feed man- and spent more time bunting, whereas those that developed agement contributes to stereotypic behavior. cribbing behavior postweaning spent 44.8 percent more time Cooper et al. (2005) observed that all horses, whether suckling and nuzzling than foals with no abnormal behavior. prone to stereotypic behavior or not, showed more stereo- The authors suggested that the extended suckling activity typic behavior as feeding frequencies of grain increased may have occurred in response to a developing gastric prob- from two, to four, to six times per day. Although high- lem or due to insufficient milk supply from the dam. As a concentrate diets were implicated as a potential cause of consequence, it was predicted that hungry foals offered cribbing (Cooper et al., 2005), cribbers spent the same creep feed might consume more concentrate feed resulting in amount of time eating as normal horses but displaced resting the gastric pathology that may stimulate cribbing. Murray time with cribbing activity (McGreevy and Nicol, 1998b). (1997) reported that 50 percent of foals have gastric ulcers Cribbers fed hay had similar concentrations of Î²-endorphin during the 1st month of life, a time period when gastric ep- to noncribbing horses, whereas concentrate-fed cribbers had ithelium is in rapid development. The use of antacids in Î²-endorphin concentrations less than half of those found in some foals not only improved gastric ulceration, but also re- normal horses (Gillham et al., 1994). This suggests that crib- duced or removed the abnormal oral behavior (Nicol et al., bing may have a neurochemical origin in addition to the pre- 2002). Thus, feed management such as use of a concentrate- disposition that may arise through nutritional management. based creep feed might aggravate an existing ulcerative con- Mills et al. (2005) recommended the following nutritional dition or predispose the foal to gastric ulceration, thereby methods for prevention of cribbing: avoid creep feeding pre- leading to abnormal oral behavior. weaning, minimize concentrates, supplement with antacid, Wood-chewing and cribbing have been associated with a or manage horses on pasture. Slightly different management lack of fiber or roughage. In addition to low-fiber intake, techniques have been posited by McBride and Long (2001), physiological changes in the gut, including a more acidic including increasing the hay ration, feeding the affected stomach pH (Lillie et al., 2003), cecal acidity (Willard et al., horse before other horses, reducing the time the horse spends 1977), and fecal acidity (Nicol et al., 2002) in cribbing in the stable, increasing its exercise, increasing social con- horses, have been implicated in these oral behaviors. Crib- tact, and using stable chain instead of a solid door so that the bing horses had a gastric pH of 3.3 compared to normal horse has a varied view from its stall. The practicality of horses whose stomach acidity was 5.5 (Lillie et al., 2003). these management tools may be difficult to implement in Prevention of cribbing using a cribbing collar eliminated the many parts of the world where feeding practices based on drop in stomach pH (pH 5.5) seen in horses that continued high-concentrate diets have been engrained or are necessary. to crib (pH 3.3) (Lillie et al., 2003). Cribbing horses have a Data are not necessarily available to support these recom-
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 223 mendations and the percentage of horses that might respond practice allows the digestive tract time to adapt to different to these interventions is unknown. levels and forms of diet, and it is especially important when feeding energy-dense diets. Large increases in daily con- centrate intakes should occur in increments over a period of GENERAL FEEDING CONSIDERATIONS several days to weeks. Although there was no experimental The goal of feeding management is to efficiently supply evidence cited, Lewis (1995) suggested that mature horses dietary ingredients in amounts that will meet the horseâs nu- should only be fed in increments of 0.2â0.3 kg concentrate trient needs, while still retaining the horseâs normal feeding per day to allow the horse sufficient time to adapt to behavior as discussed above. Meeting a horseâs dietary nu- concentrate. For similar reasons, horses should be intro- trient needs requires awareness of practices that manage duced to lush, nutrient-dense pastures by limit-grazing for feed intake and dietary ingredients that are safe, efficiently several days. utilized sources of nutrients. Reducing the rate of feed intake may be desirable if Horses are fed a variety of diets, ranging from continuous horses tend to bolt feed and to reduce competition in group- access to forage (e.g., pasture) to high amounts of concen- fed horses. Methods that have been recommended to slow trates. The type of diets fed, housing of horses, and how the feed intake in fast-eating horses include spreading grain out feeding plan integrates with other routine management prac- in shallow troughs, placing several large stones in the feed tices influences feeding management routines. Meal feeding trough requiring the horse to eat around them, or using of high-energy concentrate feeds requires intense manage- spaced bars or feeding rings to partially limit access to the ment and a large amount of control, which routinely neces- feed trough. Processing method also affects rate of intake sitates individually housing horses during feeding periods. (see Chapter 8), so moving from pelleted to textured or ex- Horses fed solely forage-based diets are felt to have a safer, truded forms of concentrates (Hintz et al., 1985) or adding more predictable feed intake because gutfill limitations will long-stem forage or short, chopped chaff (2â5 cm) can be precede the physiological controls of energy intake that con- beneficial (Harris et al., 2005; Ellis et al., 2005). trol satiety in horses fed high amounts of concentrate. Regardless of feeding system used, there are several Meal Feeding Concentrates management principles that support efficient, healthy uti- lization of diets. The first important factor in managing nu- Voluntary intake in horses appears to be influenced by a trient intake is to provide ingredients that supply a nutrition- number of factors, including weather, palatability of feed, ally balanced diet and to provide nutrients in amounts that interaction with other horses, and energy intake (see above). meet or marginally exceed nutrient requirements for the Regardless, if allowed free access to unlimited amounts, class of horse in question. Pasture should be managed to horses may consume enough starchy, nonfibrous carbohy- supply utilizable nutrients in amounts aligned with the horse drates to cause digestive upset, colic, and/or laminitis (see needs. Prepared mixes should be nutritionally balanced to specific disease entity in Chapter 12). meet needs of specific classes of horses, when fed as the Horses efficiently digest starch. Research trials cited in complete nutrient source or as a supplement to an expected Chapters 1, 2, and 8 have shown nearly 100 percent total daily intake of long-stem forage. As noted in Chapter 14, ra- tract digestion of starch. Prececal digestion of starch is at tion balancing requires knowledge of requirements, nutrient best a constant percent of ration as intake of starch is in- content of feedstuffs, feeding strategies, and physiology of creased (Hinkle et al., 1983). The more starch fed, the more horses. Common errors of on-site formulation or supple- will be presented to the microbes of the cecum and colon, mentation include making adjustments without knowledge and the more digested by these microbes. Significant of the horseâs nutrient requirements or expected intakes, levels of starch in the hindgut may cause short- and long- supplementing without knowing the amounts of nutrients al- term changes in the microbial populations, decrease intes- ready supplied by the diet, adding ingredients with little or tinal pH, disrupt normal gut motility, cause shifts in water no nutritional value, and creating dietary imbalances by ad- absorption, result in a build-up of toxins, and consequen- justing for a single nutrient with a feedstuff or supplement tially increase the incidence of laminitis and colic (Gar- that contains other nutrients. ner et al., 1978; Goodson et al., 1988; de Fombelle et al., Feeding by weight of feedstuffs rather than volume is 2004). recommended because of variation in the density of feeds With the noted ill consequences of overfeeding starch, it (see Chapter 8). As most feeding routines use volume to ap- is advantageous to determine what levels can be fed safely portion diets, it is recommended to schedule periodic checks in a meal-feeding system. Trials done with different sizes of by weighing allotted amounts. This is especially important horses and ponies ingesting different levels of starch suggest when there are changes with feed sources or with the per- that single meal starch intakes over 0.2 to 0.4 percent of sonnel assigned to feeding. body weight greatly increase the amount of starch presented Changes in the amount given or in the physical form of to the cecum and large intestine (Potter et al., 1992; Meyer dietary ingredients should be implemented gradually. This et al., 1993; Kienzle, 1994).
224 NUTRIENT REQUIREMENTS OF HORSES The level of starch in different feeds can vary greatly; horses may have increased ability to digest starch when sup- however, typical grain-based mixes may contain as much as plemental amylase is incorporated in the ration. However, 30â50 percent starch (see Chapter 2). If meals are distrib- reports are limited, and prececal starch digestion has been uted to maximize the time between feedings, confining sin- shown to be influenced by many factors, so more research gle meal intakes of a concentrate containing these amounts is necessary to clarify if Î±-amylase supplementation is of starch to below 0.5â0.6 percent of body weight per day warranted. should safely limit the meal-fed intake of starch. Those Based on the above studies and recommendations, it is horses prone to digestive or metabolic dysfunction associ- recommended to limit single-meal intakes of starch to levels ated with starch intakes should be restricted below the upper below 0.2â0.4 percent of body weight. Adjustments made to limit of a single meal of starch at 0.2â0.4 percent of body increase the nonfibrous energy concentration in the ration weight (see Chapter 8). High-quality forage diets and diets should be made gradually over several days in a step-wise containing significant amounts of digestible fiber and added fashion until targeted intakes are met. Starch intake per meal fat reduce the need for starch as an energy source. Individ- can be reduced by replacement of starch with feeds contain- ual horse responses to meal-fed concentrates will vary, and ing larger proportions of digestible fiber with added fat. additional influences such as rate of flow of ingesta, pro- cessing of feedstuffs, and addition of feedstuffs such as Feeding Forages long-stem and chopped forage will alter the suggested rec- ommendation for limiting starch levels of meals, as well as Commonly fed high-fiber feedstuffs include grain the amounts fed per meal and the meal frequency. byproducts, pasture, and harvested forage. As noted in Increased intake resulting from the feeding of low- Chapters 8 and 10, the term âfiberâ encompasses a diverse energy-dense, high-fiber feedstuffs decreases the total tract group of feedstuffs that differ in nutrient content, particle mean retention time (Cuddeford et al., 1995; Drogoul et al., size, and degree of utilization. 2001). Slowing the rate of flow of nutrients through the There are advantages for feeding diets high in fiber. The small intestine by feeding less hay or indigestible dry matter feeding of palatable harvested feeds high in fiber allows for with high-starch feedstuffs may increase prececal starch di- more continual access to feed by horses, which may reduce gestion (Meyer et al., 1993; Yoder et al., 1997). The transit boredom and stress. Vices such as wood-chewing may in- rate of high-fiber feedstuffs through the small intestine has crease when long-stem fiber is restricted. Fiber, especially been shown to be faster than when feeding similarly long-stem roughage, adds bulk to rations, which slows in- processed levels of high-starch feedstuffs (Varloud et al., take time (Argo et al., 2001). Increased dry matter intake 2004). Even so, starch disappearance in the small intestine also encourages water intake. may not be affected with differences in transit rate (Varloud As levels of fibrous compounds increase as a portion of et al., 2004). the diet, the relative amount of nonfibrous carbohydrate de- Altering the relative proportions of hay and grain and the creases. Reducing the level of starch by utilizing more fiber feeding frequency may affect prececal starch digestion. as an energy source may reduce the incidence of colic and Using the mobile-bag technique, de Fombelle et al. (2004) founder. Also, treatment of horses with certain clinical con- fed high-fiber or high-starch pellets with hay in two differ- ditions such as polysaccharide storage myopathy routinely ent feeding patterns. Similar rations were offered five times includes recommendations to reduce starch intake by feed- daily, alternating proportionate amounts of pellets and hay ing high fiber and by adding fat to rations (McKenzie et al., over a 12-h period, or three times daily by feeding two- 2003; Ribeiro et al., 2004; Valentine, 2005). thirds of the pellets in the morning, all the hay 4 hours fol- Fibrous carbohydrates are digested more slowly than lowing, and the remaining pellets at the end of the 12-hour nonfibrous carbohydrates (Argo et al., 2001). Although re- period. Transit time through the small intestine was faster search in horses is lacking, there may be a need for larger when the diets were fed five times per day; however, small particle, slower digested fiber to maintain hindgut homeo- intestine dry matter disappearance was higher when the ra- stasis. Nutritional recommendations for cattle are incorpo- tions were split into five meals. Starch disappearance in the rating minimally acceptable levels of effective neutral deter- small intestine was not affected by the two different feeding gent fiber (NRC, 2001). Physically effective neutral patterns. Prececal starch disappearance was most affected detergent fiber is a measurement used to guard against too by the botanical source of starch. high a level of small particle-sized fiber in rations. Starch digestion in the small intestine is dependent on the The need to partition the energy source away from rap- action of the pancreatic enzyme, Î±-amylase. Addition of idly digestible, highly soluble carbohydrate is even apparent supplemental amylase enzyme from bacterial sources has in some high-quality, spring-growth pastures. These pas- been shown to increase small intestinal digestion of ground tures can contain high levels of hydrolysable and rapidly fer- corn (Meyer et al., 1993). Addition of amylase enzymes has mentable fibrous carbohydrates. These levels, even when elevated the glycemic response in horses fed triticale diets fed without supplemental grain, may cause digestive upset (Richards et al., 2004), leading to conclusions that some because of too rapid a rate of hindgut fermentation (Hoff-
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 225 man et al., 2001; Longland and Murray, 2003; Watts and there are several benefits for diets based on the use of long- Chatterton, 2004). These concerns, coupled with the use of stem forage, the absolute minimal needs for intake of long- numerous byproduct feeds containing high levels of differ- stem forage is unclear. A variety of feeding strategies are ent types of fiber, emphasize the need to better define fiber used for feeding horses, ranging from all-forage diets to by partitioning into hydrolysable, rapidly fermentable, complete rations containing high levels of fiber as part of a slowly fermentable, and resistant fractions. ground, reformed, processed mix. Additional studies are Many nutritionists support the use of fiber-based rations needed to further quantify minimal needs of long-stem using long-stem harvested or growing roughage. Among the roughage. Nonetheless, because of the noted advantages of reported benefits, horses can receive a continuous supply of using fibrous sources of energy, the general guidelines of nutrients and the potential for soluble carbohydrate overload minimally supplying long-stem roughage or pasture at 1 is lessened. The question of how much fiber is minimally es- percent of body weight per day and recommending sential is not easily answered. Horses grazing pasture to roughage and pasture-based diets have nutritional merit. meet their energy needs can consume diets three times Forage-based diets guard against excessive starch ingestion higher in crude fiber than horses receiving high concentrate- by reducing or eliminating the need for concentrates. In to-forage ratio diets. Horses have been safely fed rations in many instances, forages can be offered free-choice, without research trials with as little as 11â12 percent acid detergent increasing the risk of colic or laminitis. fiber under research situations with no gastric disturbances (Yoder et al., 1997; Williams et al., 2001) and, in some feed- Managing Body Condition ing situations, especially with young, rapidly growing horses, much less. If energy supplies are in surplus, the horseâs body will There are concerns with feeding too high a level of fi- store portions of the unneeded energy as fat. If energy sup- brous carbohydrates. Some horses may require more plies are deficient, the horse will mobilize energy-containing energy-dense sources of feedstuffs to ingest sufficient en- compounds in the body and burn stored energy for fuel. Ob- ergy within limits of dry matter intake. Starch digestion in servable body fat, such as rump fat, has been used to indicate the small intestine may be more energetically efficient as total body fat (Westerfelt et al., 1976). Body condition scor- more adenosine triphosphate (ATP) is produced per glucose ing methods use fat cover to quantify the amount of body fat. molecule than when fibrous carbohydrate is catabolized to The most recognized body scoring system uniformly rates volatile fatty acids in the hindgut (Maynard et al., 1979; body condition in a scale from 1 to 9 (Henneke et al., 1983), McDonald et al., 1995). Also, there may be limits to re- as described in Chapter 1. stricting the level of particular energy-containing substrates. The optimal condition score for an individual horse de- Although research is limited and results suggest varying re- pends on the health, production, and use status of the horse. sponses, reducing starch in the diet may decrease the levels Broodmares maintained in moderate to fleshly condition of stored glucose in the body to levels that negatively affect have increased reproductive performance as compared to exercise activities that preferentially use glucose as substrate mares maintained in a moderately thin body condition (Hen- (Lawrence et al., 1991; McKenzie et al., 2003). neke et al., 1984; Morris et al., 1987; Gentry et al., 2002). There is also concern about depressing digestibility when Varying body condition scores may also affect athletic per- feeding diets containing both concentrate and long-stem formance. Energy-containing compounds in muscle may be roughage. Reports detecting negative associative effects decreased in exercising horses in thin body condition (Scott with mixed diets indicate fiber digestion may be most af- et al., 1992) and correlations between body condition scores fected (Thompson et al., 1984; Karlsson et al., 2000). Neg- and endurance race performance have been noted (Garling- ative associative effects of feeding grain with long-stem house and Burrill, 1999). roughage are not as apparent in horses as in ruminants As noted in Chapter 1, energy balance may be manipu- (Hintz et al., 1971; Martin-Rosset and Dulphy, 1987). Young lated to produce weight loss or weight gain. The most com- horses can be fed a range of hay:grain ratios and have simi- mon means of increasing energy expenditure is to increase lar growth characteristics as long as the capacity for dry activity. The most common way to facilitate weight gain is matter intake does not limit the supply of energy. Weanlings to increase energy intake. fed similar levels of nutrients with diets containing 50:50 or 35:65 hay:grain ratios have been shown to have similar Managing Weight weight and height gain and bone strength (Ott and Kivipelto, 2003). A wide variety of feedstuffs have been successfully Whether a horse is considered too fat or too thin varies be- used for growing horses (Coleman et al., 1997; Hoffman et tween different classes of horses. For example, broodmares al., 1999; LaCasha et al., 1999; Heusner et al., 2001). will typically be best managed in slightly higher body condi- The previous NRC committee provided a general guide- tion score than many growing or exercising horses. To date, line for minimal intake of long-stem roughage or pasture at there is not a universally agreed-upon definition for over- 1 percent of body weight per day (NRC, 1989). Even though weight or obesity related to body condition score in horses.
226 NUTRIENT REQUIREMENTS OF HORSES Best management guidelines for weight reduction in were initially offered at 50 percent of the calculated dietary horses will be specific to the individual horseâs health status energy need per day, and gradually increased over 10 days and history. Horses consuming high-calorie diets while re- to 100 percent. Energy density of the oat hay was lowest, ceiving little to no forced or voluntary exercise are more apt and the combined grain and hay ration highest. Horses con- to become overweight. As such, weight loss management sumed more of the grain and hay ration as compared to oat with horses should include lowering the amount of ration, hay as a percent of the amounts offered. consuming diets lower in energy concentration, and increas- Weight gains over the 10-day period were not different ing caloric expenditure through exercise. between treatments. Little to no difference was observed in Some of the frequently recommended methods for most of the measured metabolic responses: red blood cell weight reduction include reducing the levels of nonfibrous count, total bilirubin, glucose, free fatty acid, and venous carbohydrate and fat in rations by feeding higher propor- concentration of various minerals. Horses fed the grain and tions of fibrous feedstuffs. One method would be to feed hay ration had higher insulin concentrations. The general bulkier feedstuffs, such as grass hay, instead of more energy- conclusions were supportive of gradually refeeding emaci- dense concentrate mixtures. Reducing the total caloric in- ated horses with roughage-based diets. Alfalfa hay was con- take is also achieved by reducing the total amount fed of sidered to have the best results because it had a high con- meal-fed concentrates and forage. Supplementation of other centration of nutrients and less bulk than oat hay, and it nutrients will be affected with changes or decreases in intake produced a lower insulin response than the combination diet of the major ingredients of the diet, i.e., forage and/or con- (Stull, 2003). In a subsequent study, Stull (2003) compared centrate. Consequently, when diets are adjusted to reduce an alfalfa hay diet with a combination of alfalfa hay and energy intake, it is necessary to ensure adequate intake of corn oil diet when refeeding starved horses for 10 days. The other associated nutrients. Overweight horses on lush pas- addition of corn oil lowered the dietary intake of phospho- ture may require restricted grazing to adequately reduce rus, and those horses were reported to have lower blood caloric intake. It is desirable to combine dietary alterations phosphorus levels. As such, the suggestion of initially re- with structured exercise programs that increase caloric ex- feeding with alfalfa hay was reinforced. penditure. There are no proven regimens to ensure weight Nutritional programs to refeed emaciated horses should loss in horses. be coordinated with total health rehabilitation using veteri- Horses will lose weight and body condition when energy- nary assistance. Methods used to provide nutrients will de- yielding nutrients are restricted. When nutritional restric- pend on appetite, severity of emaciation, prevalence of dis- tions are prolonged, horses may become emaciated and, if ease, and advice from the attending veterinarian. Ration continued, subsequently die from starvation. Extreme amounts should be gradually introduced by closely regulat- weight loss, low body condition scores, and emaciated ap- ing intake amounts and feeding schedules. Ration amounts pearance are usually associated with insufficient energy or should be offered initially in small amounts and frequent protein. However, malabsorption, parasitic infestations, old feedings. Generally, use of high-fiber feedstuffs is preferred age, senility, and various diseases also lead to emaciation for the initial refeeding period. Uniformly accepted prac- (Kronfeld, 1993). As such, nutritional programs must be co- tices are largely unavailable, partially because of limited ordinated with the correct diagnosis of the cause and with amounts of controlled research and clinical reports, the spe- the total rehabilitation procedures. Nutritional programs to cific nature of individual cases, and the variety of associated rehabilitate emaciated horses should consider the adminis- medical conditions that are possible. tration route, physical form, and nutrient content of the nu- tritional support. If the horse is unable or unwilling to eat, ENVIRONMENTAL CONSIDERATIONS intragastric administration or enteral support may be the only alternatives. Most dietary nutrients that are not retained in the body If the horse is willing and able to eat, nutritional pro- are excreted in the urine and feces. Therefore, the nutrient grams must consider the physical form and nutrient profile composition of the diets consumed by horses will affect the of the diet, and patterns and level of intake. As such, recom- amount and composition of waste excreted by horses into mendations tend to vary between reports, including the need the environment (Topliff and Potter, 2002). The desire to to adjust procedures based on animal response, and are feed diets that maximize production and performance is un- somewhat qualitative in nature. Regardless, nutritional pro- derstandable. No one wants to feed a diet that prevents a grams for starved or emaciated horses should be aligned horse from achieving its genetic potential. However, diets with the total rehabilitation program, thus emphasizing the are regularly formulated to cover any potential shortfall of need for frequent, close veterinary care and intervention. most nutrients on a âworst case scenarioâ basis, often with Witham and Stull (1998) have reported on the metabolic little regard as to the environmental impact. The goal of this responses of chronically starved horses re-fed with either al- section is to review the current environmental regulations falfa hay, oat hay, or a combination of oat hay and an ex- that pertain to horses, horse owners, and horse facilities and truded, complete commercially prepared ration. The diets to further heighten awareness of the specific areas where
FEEDING BEHAVIOR AND GENERAL CONSIDERATIONS FOR FEEDING MANAGEMENT 227 horses may contribute significantly to the nutrient and patho- nitrate. This nitrogen usually stays with the manure until gen load in the environment. spread on pastures or composted. When manure is spread in a fresh state, the nitrates can leach into ground water or run off into surface water. Nitrates have been associated with Current Regulations âblue babyâ syndrome in humans (US EPA, 1999). The EPA The U.S. Environmental Protection Agency (EPA) pro- has set the allowable limits of nitrates in ground water at mulgated new regulations under the Clean Water Act (CWA) 10 mg/L. Many rural water supplies now exceed this limit in 2003 (40 CFRâChapter 1âPart 122). These new regula- and those communities have been forced to search for new tions update the definition of Animal Feeding Operations supplies. The exact source of these nitrates has not been (AFO) and regulation of certain AFOs as Concentrated An- identified. Although it is likely that nitrogen fertilizers are a imal Feeding Operations (CAFO). The regulations contain significant contributor, livestock waste may contribute as provisions that have potentially serious implications for the well. Composting of manure is often touted as a solution; horse industry. The EPA has adopted a three-tiered plan for however, much of the nitrogen fraction in composted ma- regulation of CAFOs that classify them as Large, Medium, nure is volatilized and released depending on the degree of or Small and places the number of confined horses neces- composting. The result is a nitrogen:phosphorus ratio that is sary to qualify for a particular status at 500 and 150 for the very low, necessitating the use of an additional nitrogen Large and Medium categories and authority of regional di- source to support ideal plant growth (Havlin et al., 1999). rectors to specify operations for the Small category. Any Some of the nitrogen is captured in the organic matter and is AFO that discharges pollutants directly into the waters of often termed organic nitrogen. It tends to be released very the United States or has animals in direct contact with wa- slowly and is less available to support plant growth. ters of the United States may be designated as a CAFO re- Of the minerals found in fecal material, phosphorus is gardless of the number of animals confined. Data were pro- generally of greatest concern. It is usually found in the high- vided to EPA from the American Horse Council (Topliff and est concentration and is the most stable and mobile of the Potter, 2002) in response to a Notification of Data Avail- minerals. Phosphorus in the form of phosphate is soluble in ability (NODA), requesting that horses be counted in the water and moves freely among soil particles. Surface appli- same manner as feedlot cattle; however, the EPA chose to cation of manure in high-rainfall areas results in surface continue counting each horse as two animal units. Thus, any water contamination that is usually manifested as algae operation that has 150 or more horses in confinement (in- blooms in streams and rivers. As the algae growth proceeds cluding stalls or drylots) for a total of 45 days or more in any unchecked, the dissolved oxygen levels in the water decline 12-month period or is otherwise designated as a CAFO has and massive kills of marine and aquatic life can occur. Phos- a duty to seek coverage under a National Pollution Dis- phorus concentrations are not significantly affected by com- charge Elimination System (NPDES) permit. Many stables, posting, which, as previously stated, necessitates the addi- breeding farms, and exhibition facilities that have not previ- tion of nitrogen to produce a balanced fertilizer product. In ously been affected may now have to meet the requirements some areas of the United States, the phosphorus content of of the new regulations, including a provision to be able to the soil is sufficient to support plant growth for the next 100 contain all of the runoff from a 25-year, 24-hour storm event. years. In many areas, the problem is so severe that it is cur- rently illegal to apply manure or commercial fertilizers con- taining phosphorus to that land. Effects of Diet Composition on Nutrient Excretion Other minerals are also of concern. Copper and zinc are The main environmental challenges created by animals toxic to certain aquatic microorganisms and will likely be- and their waste products are nitrogen, minerals, fecal bacte- come a target for nutrient management plans. Sodium is ria, and land erosion from overgrazing. Nitrogen is elimi- contained mostly in the urine and can reach significant con- nated from the horse as urea in the urine and protein in the centrations in composted manure. In some areas of the feces. Urea is easily converted to ammonia, a volatile and United States, the sodium content of surface water is be- toxic gas, by urease, an enzyme that is abundant in the envi- coming problematic. In those areas, water is being blended ronment. Ammonia is a health concern to horses as well as from several sources to achieve a sodium level acceptable to humans. High ammonia concentrations in stalls have been for drinking (US EPA, 1996). associated with upper respiratory disease and poor perfor- Bacteria of fecal origin are currently a major health con- mance in horses (Pratt et al., 1999). Additionally, ammonia cern. Recent disease outbreaks from Escherichia coli, Liste- is a significant contributor to the particulate matter (PM) 2.5 ria, and Salmonella that have resulted in the deaths of chil- load in the atmosphere. The designation 2.5 refers to fine dren and the elderly have heightened the awareness of particles less than 2.5 micrometers in diameter. This aspect animal waste. Horses are not likely a source of the most of air quality is one that is relatively new, but one that has deadly E. coli strain (0157:H7) or of Listeria, which is serious consequences for the animal industry. The nitrogen found mainly in sausage-type products. Horses do, however, found in feces is mostly in the form of microbial protein and harbor Salmonella. One study estimated that 80 percent of
228 NUTRIENT REQUIREMENTS OF HORSES all horses harbor Salmonella and that up to 20 percent are If land application is not possible, such as in urban or active shedders (NAHMS, 2001). Certainly the opportunity suburban settings, waste may need to be taken to a landfill. for transmission to the human population exists. Clostridium Owners should check local laws and regulations concerning spp. may also pose zoonotic risks but are uncommon inhab- this practice and may need to hire a commercial firm to dis- itants of the feces of normal horses, although moderately pose of the waste. prevalent in diarrheic horses (Garrett et al., 2002). There are In spite of the method of waste disposal chosen, horse proposals circulating within regulatory agencies that would owners have the opportunity to be more environmentally require fencing of all riparian waterways from all livestock friendly by feeding horses as closely to their nutrient re- and establishment of filter strips along those waterways that quirements as possible. Feeding diets that are excessively would take up nutrients from potential runoff. high in protein and minerals, particularly phosphorus, cop- The final environmental challenge is soil erosion as a re- per, and zinc, puts the industry at significant risk for regula- sult of overstocking, overgrazing, and undermanagement. tion by federal agencies in the future. While the small horse owner with limited land area is the most often seen example, large reputable breeding farms are REFERENCES often guilty as well. If the Total Maximum Daily Load (TMDL) standards are adopted as currently proposed by Aiken, G. 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