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13 Donkeys and Other Equids DONKEYS (ASSES, BURROS, EQUUS ASINUS) in nitrogen (Pearson et al., 2001). Suhartanto and Tisserand (1996) showed that the donkey was more able than the pony Feeding Behavior to use forages, even poor-quality forages. The authors indi- cated that the superiority of the donkey results from a higher The donkey is a unique equid of special qualities, an evo- feed intake, higher capacity to sort feed, lower water need, lutionary relative of the horse that will forever be compared and more developed system to recycle blood urea. with the horse (Burnham, 2002). However, the donkey is morphologically and behaviorally distinct, and presumably Dry Matter Intake evolved in a hot semi-arid environment (Mueller et al., 1994a). Most likely, the domestic donkey originated from Mediterranean miniature donkeys fed a diet consisting the African wild donkey (Equus africanus, Nubian or So- mainly of Bermudagrass hay (80 percent of total diet) plus mali subspecies; Groves, 1974). Mules (a cross between the supplements (electrolytes and chelated minerals) at 1.5 per- mare and the jack) and hinnies (the reciprocal cross between cent of body weight (BW) maintained good health status jennets and stallions, but that are seldom found) are major and an average target BW of 111 Â± 1.3 kg for a long period sources of power in many regions of the world because of of time (e.g., more than 2 years: Schlegel et al., 2004). Some their astounding strength, endurance, and heat tolerance studies that have compared feed intakes of donkeys and (Cole and Ronning, 1974). ponies fed moderate- to low-quality roughage have shown Feral donkeys are known to be highly adaptable feeders that donkeys generally consume less dry matter/day than that will consume a variety of grasses, browse, and forbs in ponies. On the contrary, some authors have suggested that order to obtain sufficient nutrients. In Botswana, donkeys dry matter intake (DMI) of donkeys is high compared to consume browse such as Boscia foetida and Acacia species other large herbivores, at about 3.1 percent of body weight during the long dry season when the nutritive value and the (Maloiy, 1973). Pearson (1991) and Pearson et al. (2001) re- quantity of the grasses are poor (Aganga and Tsopito, 1998). ported voluntary dry matter intakes (VDMI) that ranged Donkeys will peel the bark off and consume the bark and the from 0.83 to 2.6 percent of BW, depending on the type of succulent layers underneath. Donkeys use different feeding feed and physiological stage of the animal. Svendsen (1997) strategies, depending on the quality of the feed. Thus, they indicated that DMI of feed as a percentage of body weight will use a selective feeding strategy targeting high-quality should be 1.75â2.25 percent to meet the metabolic demands bites when foraging over a mixed pasture or rangeland, but for maintenance for most donkeys and mules. When don- when fed homogenous hay, donkeys will maximize intake as keys and ponies were fed moderate- and/or poor-quality for- an alternative feeding strategy (Mueller et al., 1998). age diets, donkeys consumed less dry matter per day (Pear- It is generally accepted that the donkey can exist with less son and Merritt, 1991). The authors found that the feed than the horse. Donkeys and mules can utilize more digestibility coefficients of organic matter and fiber frac- mature, less digestible, woodier plant material than a horse tions (acid detergent fiber, ADF, and neutral detergent fiber, (Svendsen, 1997). A report by Yousef (1985) indicated that NDF) were higher (P < 0.05) for the donkeys than for the two donkeys maintained good health during 12 years on a ponies, and higher for the alfalfa hay than for the oat-straw diet consisting only of grass hay. In confinement in tropical diet. Greater DMI by ponies (P < 0.01) compensated for the countries, a donkey diet will consist of crop residues and lower digestibility coefficients, suggesting that both species mature grasses of poor nutrient quality, high in fiber and low obtain similar quantities of nutrients if diets were fed ad li- 268
DONKEYS AND OTHER EQUIDS 269 bitum. Studies by Pearson et al. (2001) reported intake of The differences were greater on the oat-straw diet than on dehydrated alfalfa by donkeys of 27 g/kg BW, higher than the alfalfa diet (Pearson et al., 2001). Similar observations previously reported values for donkeys consuming grass and have been previously reported in comparative studies with grass-legume hay mixtures (18â23 g/kg BW: Pearson and straw and alfalfa diets (Pearson and Merritt, 1991; Pearson Merritt, 1991; Tisserand et al., 1991; Mueller et al., 1994b). et al., 1992; Cuddeford et al., 1995). Pearson and Merritt Donkeys fed 1 kg of concentrate plus ad libitum dry (1991) found that at rest, when ponies and donkeys had ad chopped sorghum fodder consumed 23 g/kg BW (resting libitum access to a hay or a barley-straw diet, ponies con- donkeys) and 29 g/kg BW (working donkey), respectively sumed more (P < 0.01) on a g/kg BW/d basis than donkeys, (Ram et al., 2004). For donkeys fed straw-type diets, reports but donkeys showed higher digestibility coefficients for dry indicated consumptions of 20 g/kg BW of oat straw and 9.8 matter, organic matter, and energy. g/kg BW of barley straw (Pearson et al., 1992; Pearson and The mean retention time (MRT) of alfalfa and straw-type Merritt, 1991). Donkeys (mean BW of 243 kg) showed diets is shorter in the donkey (BW range 117â129 kg) than higher (P < 0.01) DMI (14.7â16.5 g/kg) than ponies in the Bedouin goat, consistent with its capacity to compen- (9.7â11.14 g/kg, mean BW of 200 kg) of wheat-straw-based sate for a lower quality diet by increasing its intake rate diets (Suhartanto et al., 1992). However, comparative stud- (Izraely et al., 1989b). Mean retention time of digesta parti- ies of voluntary DMI of donkeys and ponies fed moderate- cle markers by the digestive tract of donkeys fed a wheat- to low-quality forage have shown that donkeys generally straw or alfalfa-based diet were 37.7 Â± 1.7 hours and 36.4 Â± consumed less dry matter per day than ponies (Pearson and 3.2 hours, respectively. Furthermore, the transit time Merritt, 1991; Tisserand and Pearson, 2003). Intake of (marker first appearance in feces) was 16.8 Â± 3.7 hours and cocksfoot/alfalfa hay by donkeys was 87 percent lower than 17.5 Â± 2.6 hours when fed the wheat straw or alfalfa hay, re- that observed in ponies (Tisserand et al., 1991). Summer and spectively (Izraely et al., 1989b). Gastrointestinal transit winter DMI of grass/straw mixed diets were 64 and 69 per- time was significantly (P < 0.01) slower in the donkeys than cent of those calculated for ponies (Wood et al., 2005). in the ponies on both meadow hay and barley-straw diets When donkeys (n = 18, mean BW: 150 kg for males and (Pearson and Merritt, 1991). Similar results have been re- 142 kg for females) had ad libitum access to water, or were ported by Cuddeford et al. (1995), who found consistently offered water every 48, or every 72 hours, DMI of a poor- slower rates of passage of the solid-phase marker for all quality diet (6 percent crude protein [CP], 78 percent NDF, diets given to donkeys compared to other equids (P < 0.01). 46 percent ADF) were 3.1 Â± 0.2, 2.8 Â± 0.1, and 2.7 Â± 0.1 The level of feeding and the forage type influenced the di- kg/d, respectively, indicating that water restriction did not gestibility of forages by donkeys and ponies. Dry matter di- affect DMI considerably (Nengomasha et al., 1999). Gross gestibility was higher when offered ad libitum access to an energy consumption was 81 Â± 17 kcal/kg BW/d for donkeys oat-straw diet compared to when it was restricted, especially (BW ranging between 117â129 kg BW), which was 67 per- in the donkey, which might be explained by improved selec- cent lower than when the animals received an alfalfa hay tion of more digestible components in the oat-straw diet by diet (Izraely et al., 1989a). this species (Pearson et al., 2001). The relatively narrow muzzle of the donkey as compared to the horse would indi- cate selectivity to be a characteristic of its feeding strategy Apparent Digestibility of Nutrients (Van Soest, 1994). Tisserand et al. (1991) also indicated that It has been suggested that because of the differences in donkeys tended to have higher digestibility coefficients of the ways in which donkeys and ponies consume and digest the dietary components (e.g., crude protein, crude fiber, and feeds, the donkey cannot be regarded as a small horse when organic matter) than ponies. Digestive coefficients for ADF considering its nutrition (Tisserand and Pearson, 2003). and NDF when donkeys were fed a wheat-straw diet were Thus, Izraely et al. (1989a) reported that the energy di- 42 Â± 4.1 and 50.9 Â± 4.9 percent, respectively, and 46.8 Â± 4.8 gestibility of low-quality forage in donkeys matched that and 54.2 Â± 1.4 for ADF and NDF, respectively, when don- recorded for the Bedouin goat and exceeded that when don- keys were fed an alfalfa hay diet (Izraely et al., 1989b). keys were fed an alfalfa hay diet (Brosh et al., 1986). Izraely More effective microbial digestion in the hindgut of the et al. (1989a) reported digestible energy (DE) coefficients donkey compared to the pony might be the reason for the for donkeys of 49 Â± 4 and 67 Â± 3 percent for wheat-straw higher digestibility coefficients. The microbial cellulolytic and alfalfa diets, respectively. activity in the cecum was higher by 13 percent in donkeys The digestibility coefficients of the main dietary compo- than in ponies when animals were fed a mixed cocksfoot/ nents of forages measured in donkeys were higher than alfalfa hay or wheat straw hay (Suhartanto et al., 1992). those measured when the same feeds were fed to ponies and When wheat straw was fed with or without concentrate, the horses (Araujo et al., 1997). When donkeys were fed an al- authors observed higher (P < 0.001) volatile fatty acids falfa or oat-straw diet, donkeys showed higher digestibility (VFA) production (mmol/L) in donkeys (47â67.1) than in coefficients (percent) than ponies for DM, organic matter ponies (33.6â41.9). Furthermore, the authors found that the (OM), gross energy (GE), CP, ADF, and NDF (P < 0.05). proportion of VFA (percent molar) indicated that the con-
270 NUTRIENT REQUIREMENTS OF HORSES centrations of butyric, isobutyric, valeric, and isovaleric kcal/kg BW) maintained a healthy average body weight acids were higher (P < 0.01) in donkeys than in ponies. In (111 Â± 1 kg; range: 110â112 kg) for 3 years (Schlegel et al., contrast, acetic acid values were not significantly different 2004). However, the DE maintenance requirements were (69.3 vs. 72.8 mol percent) between donkeys and ponies, re- overestimated by 16.7 percent (4.73 Mcal/d) based on the spectively. Dry matter intake, dry matter digestibility Pagan and Hintz (NRC, 1989) formula for horses weighing (DMD), and MRT of a poor-quality diet were not signifi- 600 kg or less (DE (Mcal/d) = 1.4 + 0.03 Ã BW). Thus, the cantly different for working or nonworking donkeys (Nen- original Pagan and Hintz (1986a) formula to estimate DE gomasha et al., 1999). maintenance requirements might be adjusted for these miniature donkeys as: DE (Mcal/d) = 0.61 + 0.03 Ã BW (in kg). If Equation 13-1 above is applied to these miniature Energy donkeys, the DE requirements are underestimated by 13 per- Guerouali et al. (2003) and Tisserand and Pearson (2003) cent. Taylor (1997) suggested that the energy requirements indicated that a donkeyâs resting metabolism is 20 percent of donkeys are of the order of 75 percent of those published lower (P < 0.05) than that of a horse and that donkeys re- for horses per unit body weight. quire less feed over the working year than horses or cattle due to their small size. On a mass specific basis, oxygen Energy Cost of Work consumption at rest were 3 Â± 0.2 and 3.2 Â± 0.3 ml/kg BW/min for horses and donkeys, respectively (Guerouali et Walking with a load averaging 40 percent of their body al., 2003). Donkeys altered resting metabolic rate in re- weight 8 h/d increased the daily energy consumption by sponse to diet quality. Thus, the resting oxygen consumption 60â70 percent for both donkeys and horses (Guerouali et al., of donkeys fed wheat straw was 4 Â± 0.2 L/kg BW/d, half the 2003). Oxygen consumption (VO2) in donkeys running at a value recorded when donkeys were fed alfalfa hay (Izraely maximal speed on a 9.8 percent slope was 110 Â± 2 ml Ã et al., 1989a). Walking for 8 h/d increased the daily en- minâ1 Ã kgâ1, 22 times pre-exercise VO2 (Mueller et al., ergy expenditures by 60â70 percent in donkeys and horses 1994a). Donkeys are more efficient at using energy for (Guerouali et al., 2003). pulling and carrying loads, but their small size restricts the There is a lack of information on the DE requirements size of the load (Pearson et al., 1996). Average energy for specific for donkeys. However, recent reports by Wood et al. donkeys under 0 or â15 percent slope were 0.23 and 0.16 for (2005) indicated that donkeys (n = 20, BW ranged from walking, 0.26 and 0.79 for carrying a load, and 6.3 and 1.5 133â217 kg) fed hay:straw mixed diets required consider- cal/m/kg for pulling loads, respectively (Dijkman, 1992). ably less DE intake for maintenance than ponies when using Vall (1996, as reported by Tisserand and Pearson, 2003), NRC (1989) equations. Their results indicated that DE in- working with donkeys (150 kg BW) and ponies (250 kg take was 54 and 74 percent of recommendations for summer BW) that were subjected to work for 10 km on level ground and winter diets, respectively (Wood et al., 2005). at a draught force of 200 Newtons (N) (light cart, LC) or 350 Researchers have applied equations developed for horses N (cultivator for weeding, CW), found that the daily net en- to estimate DE requirements of donkeys. However, these ergy requirement (DNER, Mcal/d) and net energy used for equations might overestimate requirements as indicated work (NEW, Mcal/d) for donkeys on a LC and CW load above. Pearson et al. (2001), has applied the following equa- were 4.6 Mcal and 1.7 Mcal, and 5.6 Mcal and 2.6 Mcal for tions to estimate DE requirements: DNER and NEW, respectively. The values for LC and CW reported for the ponies were 6.7 Mcal and 3.1 Mcal and 5.6 (a) Maintenance requirements Mcal and 2.0 Mcal for DNER and NEW, respectively. The (Equation 13-1): DE Mcal/d = (0.975 + 0.021 Ã M), authors reported the net energy cost of work as a multiple of where M = live body weight in kg (NRC, 1989) the maintenance energy requirements. For the donkey, these (b) Maintenance requirements for ponies values were 0.57 and 0.91 for the LC and CW loads; for the (Equation 13-2): DE Mcal/d = (465) Ã M0.75/4184, pony, these values were 0.56 and 0.85, respectively (Vall, where M = live body weight (Ellis and Lawrence, 1996, as reported by Tisserand and Pearson, 2003). In stud- 1980, original units in MJ) ies conducted by Yousef and Dill (1969) and Yousef et al. (1972), in which donkeys were compared to men, the energy When Pearson et al. (2001) applied Equation 13-2 to cal- cost of walking with or without a load and up and down culate DE intake, the authors reported that intake of straw- grades, in terms of units body weight and unit distance, was based diets fed ad libitum exceeded pony energy require- significantly lower in the donkey. The low energy cost of ments by 34 to 51 percent (9.6 Mcal/d), but energy walking and the associated economy in food and water re- requirements of donkeys were only just met (5.6 Mcal/d). In quirements appear to be key mechanisms for the donkey to their study, the estimated DE requirements were 7 Mcal/d thrive in arid regions (Yousef, 1985). Table 13-1 summarizes and 5.7 Mcal/d for ponies and donkeys, respectively. Minia- information on energy expenditures on horses and donkeys ture Mediterranean donkeys fed a diet of 3.94 Mcal/d (35.5 (adapted from Guerouali et al., 2003).
DONKEYS AND OTHER EQUIDS 271 TABLE 13-1 Comparative Energy Expenditures in Environmental Stress: Heat Stress and Dehydration Horses and Donkeys (adapted from Guerouali et al., 2003)a In Somali donkeys, complete deprivation of water under Resting Walking an environmental temperature of 22 Â± 2Â°C depressed food in- Resting (R) with Load Walking with Load take by 83â90 percent by the end of 8â12 days (Maloiy, Horses 21 Â± 0.8 29.4 Â± 1.8 35.3 Â± 2.1 42.0 Â± 0.6 1973). In the same study, a 15 percent level of dehydra- (kcal/kg BWb) tion at 22 Â± 2Â°C depressed feed intake by 30.4 percent (P < 0.001) to 2.13 kg/100 kg BW/d of a low-quality hay diet Multiple of R â 1.4 1.7 2.0 that simulated the natural diet available during the dry season Donkeys 22 Â± 1.3 26.4 Â± 3.3 39.6 Â±2.6 46.2 Â± 0.3 in the desert of Eastern Africa. However, the apparent di- (kcal/kg BWc) gestibility of DM at 22 Â± 2Â°C increased on dehydration from 41 percent to 51 percent in Somali donkeys. Dehydration Multiple of R â 1.2 1.8 2.1 under simulated desert conditions (22â40Â°C) had no effect aDonkeyâs average BW: 120 kg; horses average BW: 310 kg; original units on apparent digestibility (51 percent), although feed intake in kJ/kg0.75 (1 kJ = 0.239 kcal); load weight corresponds to an average 40 was depressed by 26.8 percent to 2.24 kg/100 kg BW percent of BW; horses and donkeys fed a diet of 1 kg barley and 2 kg (Maloiy, 1973). The donkey has an exceptional tolerance to straw/100 kg BW; donkeys: n = 4; horses: n = 2. Experimental design based on the measurement of oxygen consumption during four successive periods dehydration that in part can be explained by its ability to con- of 15 minutes each (resting, resting with load, walking, walking with load). serve blood volume. This helps maintain circulation, dissipa- bOriginal data for resting energy expenditure in horses was 15.18 Â± 0.57 tion of heat, and salivary flow (Yousef et al., 1970). This kJ/kg0.75/h. might explain the well-being of donkeys after a degree of de- cOriginal data for resting energy expenditure in donkeys was 12.64 Â± 0.73 hydration that would cause dehydration exhaustion in many kJ/ kg0.75/h (Guerouali et al. 2003). other mammals. El-Nauty et al. (1978) indicated that dehy- dration significantly decreased resting metabolic rate (VO2) in donkeys at environmental temperatures ranging from 20 to 35Â°C. The low resting metabolic rate in dehydrated animals Protein is an adaptive mechanism to reduce water need for ther- moregulation. Donkeys exposed to environmental tempera- There is a lack of information on the protein requirements tures ranging from 7 to 45Â°C increased skin evaporative for donkeys, but apparently donkeys are very efficient in the water loss significantly at temperatures above 30Â°C (Maloiy, utilization of dietary protein. Izraely et al. (1989a) found that 1971). Yousef (1991) reported that the adaptation of donkeys donkeys fed a wheat-straw diet containing less than 3 percent to arid conditions are due to (1) its economy in the use of crude protein maintained body weights for a prolonged pe- water such as reducing sweating and water excretion; (2) the riod of time and their capacity to recycle urea matched that ability to support dehydration, within limits, without negative showed by ruminants. Furthermore, when fed a wheat-straw effect; and (3) its capacity to fully rehydrate within a few diet, the amount of nitrogen recycled exceeded that con- minutes of availability of water. The donkey has an impres- sumed in the diet (Izraely et al., 1989a). The donkey reab- sive capacity for rehydration. One study indicated that burros sorbed 82 percent and 48 percent of the urea filtered by the ingested water at a rate of about 17â20 percent of body kidney when fed a wheat-straw or alfalfa hay diet, respec- weight within 5 minutes, without ill effects (Yousef et al., tively. Expressed as percentage of the entry rate, the urea ni- 1970). The donkeyâs capacity to fully rehydrate within 1.5 trogen recycled when on wheat-straw averaged 76 percent of hours (recovery period) after being subjected to 36 hours of the urea nitrogen entry rate (Izraely et al., 1989b), matching water deprivation has been also reported by Mueller and Bedouin goats living in desert environments (Brosh et al., Houpt (1991). The same authors reported that ponies de- 1986, 1987). The efficient utilization of dietary protein, a prived of water during 36 hours, when offered water, under- high true nitrogen digestibility of 86â90 percent, and the compensated for the water deficit. The donkeyâs long ears, high capacity to retain and recycle urea creates the ability for relatively small body, long legs, and short hair help its adap- the donkey to subsist on low-protein forage (Izraely et al., tation to hot climates (Cole and Ronning, 1974). 1989a,b). Pearson (1991) used the formula digestible crude protein (DCP)(g/d) = 2.7 BW0.75 (NRC, 1978) to estimate di- gestible protein requirements for donkeys ranging from Water Consumption 160â190 kg BW. Miniature donkeys that consumed 1.2 g CP/kg BW (133 g of protein/d) fed an 8 percent crude pro- The donkey is credited with the ability to continue eating tein diet (DM basis), comprised nearly entirely of Bermuda- for several days when deprived of drinking water (Dill et al., grass (80 percent), maintained body weights for a prolonged 1980). Maloiy (1970) suggested that donkeys can conserve period of time (Schlegel et al., 2004). Mueller et al. (1994b) body water and avoid thirst by reducing sweating for ther- suggested that crude protein requirements of donkeys lies be- moregulation and reduced fecal water loss via increased in- tween 3.8 and 7.4 percent of the diet (DM basis). testinal sodium resorption. Donkeys have lower water re-
272 NUTRIENT REQUIREMENTS OF HORSES quirements per unit of BW than other domesticated animals, are abundant and of good quality. In contrast, emaciation is with the exception of camels (Aganga et al., 2000). Water the biggest problem facing donkeys in tropical areas where turnover rates of 88 Â± 18 ml/kg BW/d and 115 Â± 9 ml/kg food is scarce and of poor quality and where donkeys are BW/d were reported in donkeys (average BW 123 kg) fed required to work (Svendsen, 1997; Pearson and Quassat, wheat-straw or alfalfa hay, respectively (Izraely et al., 2000). Body condition scoring (BCS) systems have been 1989a). It seems reasonable to attribute this ability of the developed by Vall et al. (2003b) and Pearson and Quas- donkey to its desert inheritance. Dill et al. (1980) suggested sat (2000), the latter modeled on a 9-point system that donkeys might be able to store water in their gastroin- (1-emaciated, 2-thin, 3-less thin, 4-less than moderate, testinal tract that will help buffer against decreased water in- 5-moderate, 6-more than moderate, 7-less fat, 8-fat, 9-obese) take. However, in more recent studies by Mueller and Houpt developed originally for zebu cattle. The BCS described by (1991), in which comparisons were made between donkeys Vall et al. (2003b) has been developed for working donkeys and ponies subjected to 36 hours of water deprivation, no and the score is given for the donkeyâs back and flank on a differences were found between the two species when blood scale of 1 to 4 (1-emaciated, 2-thin, 3-average, and 4-good). variables (packed cell volume, plasma protein, plasma os- Donkeys tend to accumulate fat on the neck, on either side of molality) were used to assess dehydration. When water was the chest wall giving a saddlebag appearance, and around the offered ad libitum, donkeys (n = 18) fed a low-quality diet buttocks (Svendsen, 1997). Estimation of body weight in (6 percent CP, 78 percent NDF, 46 percent ADF/DM basis) working donkeys (n = 500) from body measurements have drank an average of 8.5 Â± 0.64 L/d (Nengomasha et al., been developed by Quassat et al. (1994): 1999). In the same study, if donkeys were offered water every 48 or 72 h, water intakes were (heart girth, cm)2.12 Ã (length, cm)0.688 4.9 Â± 0.41 and 5.1 Â± 0.4 L/d, lower (P < 0.001) if water was Weight (kg) = ââââââââââââââââ offered on an ad libitum basis. Ponies (BW: 266 kg) con- 3,801 sumed (P < 0.001) more water than donkeys (BW: 197 kg) when fed an alfalfa-based diet (4.35 vs. 3.21 L/kg DM). where length = length of the body from the pin bone (tuber Similar results were found when ponies (BW: 254 kg) and ischii) to elbow in a straight line in centimeters (cm) and girth donkeys (BW: 182 kg) were fed an oat-straw diet (3.77 vs. is the measurement around the body just behind the front 3.18 L/kg DM, for ponies and donkeys, respectively: Pear- legs, in centimeters (cm). Donkeys used in this study ranged son et al., 2001). When donkeys (BW: 185â250 kg) were of- from 74â252 kg BW, height from 82â129 cm, length from fered water on ad libitum basis, they consumed 64â106 cm, and body condition from 2â7, as indicated above. 8.3 Â± 0.6 L/d when fed a mixed hay diet, but if donkeys were deprived of water for 36 hours, the water consump- Chemical Composition of Donkeyâs Milk tion dropped to 6.8 Â± 0.6 L/d (Mueller and Houpt, 1991). Vall et al. (2003a) recommended that resting donkeys in The composition of donkeyâs milk is given in Table 13-2. Cameroon (average BW: 125 kg) be offered 12 liters per day of water in the cool season and 15 liters per day in the Blood Variables hot dry season. Ram et al. (2004) reported water intakes be- tween 8.4 Â± 0.47 L/d (resting donkeys) and 13.25 Â± 0.64 L/d There are not much published data on mineral and vita- (working donkeys) for animals that ranged in weight from min concentrations in the serum or plasma of donkeys. 130â154 kg BW and under environmental temperatures that Schlegel et al. (2004) found plasma levels of 2.53 Â± 0.61 varied between 28 and 32Â°C and relative humidity of 64â70 Âµg/ml of Î±-tocopherol (average of three samples collected percent. Donkeys had lower (P < 0.05) water intakes (1.93 between 1999 and 2004) in miniature donkeys (n = 2) that L/kg DM) than Shetland ponies (2.4 L/kg DM), and both fell within the recommended values for domestic equids ponies and donkeys had lower water intakes (P < 0.01) than (2â10 Âµg/ml: Puls, 1994). The same authors reported an av- Thoroughbreds (3.87 L/kg DM) or Highland ponies (4.22 erage (n = two samples) plasma concentration value of L/kg DM: Cuddeford et al., 1995). Mueller et al. (1994b) re- 0.169 Â± 0.046 Âµg/ml for vitamin A (retinol) that was mar- ported that under conditions of high ambient temperature ginally lower than reference values for domestic horses (25â37Â°C), donkeys consumed water at a rate of 9 percent (0.175â0.35 Âµg/ml: Puls, 1994). of BW/d compared to donkeys in temperate regions that consumed water at a rate of 4â5 percent of BW/d even if fed Practical Diets high amounts of DM and NDF. Donkeys are fed different diets based on their geograph- ical location. Thus, in tropical and arid regions, they are fed Body Condition Score in Donkeys on crop residues and mature grasses consisting of low- Obesity is the biggest challenge facing nonworking don- protein and high-fiber contents for most of the year. Mainte- keys kept in temperate areas of the world where food sources nance requirements can be met from forage alone for most
DONKEYS AND OTHER EQUIDS 273 TABLE 13-2 Chemical Composition (g/100 ml) of Milk of Donkeys and Other Animal Speciesa Milk Source Lipid Protein Lactose Total Solids Ash Donkey 0.38 (1.34) 1.72 (1.94) 6.88 (6.29) 8.84 (10.24) 0.39 (0.43) Horse 1.36 2.10 6.16 10.04 0.42 Horseb 0.74 2.16 6.62 10.44 0.44 Cow 3.70 3.20 5.00 12.70 0.80 Goat 4.00 3.10 4.25 12.05 0.80 aAdapted from Miraglia et al. (2003). Figures in parentheses represent numbers for donkeys reported by Salimei et al. (2000, as reported by Miraglia et al. 2003). bAdapted from Pagan and Hintz (1986b). donkeys and concentrate feeds are offered only in situations However, the calculated DE intakes indicated in Table where donkeys cannot eat sufficient forage to meet nutrient 13-4 are much higher than the recommended values for requirements, such as those in work and those that are preg- horses determined using the Pagan and Hintz equation nant, lactating, growing, or elderly (Taylor, 1997). Table (NRC, 1989). For example, miniature donkeys weighing an 13-3 indicates recommended forage:concentrate ratios and average of 111 kg, as previously indicated, can be main- daily DMI for adult donkeys as reported by Pearson (2005). tained on a diet of 35.5 kcal/kg BW (3.94 Mcal/d). The ad- Applying the DMI and forage:concentrate ratios values justed Pagan and Hintz equation (1986a) for miniature don- from Table 13-3, nutrient intakes for adult donkeys can be keys under maintenance conditions as reported above (DE: estimated (Table 13-4). Mcal/d = 0.61 + 0.03 Ã BW) can be used for better predict- TABLE 13-3 Daily Rations for Adult Donkeysa Body Weight Total DMIb Forage Concentrate State kg kg Poor, kg Good, kg kg Mature idle 200 5 4.5 â 0.5 Mature idle 200 5 â 5.0 â Work 4 h/d 200 4 1.6 â 2.4 Work 4 h/d 200 4 â 2.0 2.0 Lactationc 200 4 1.2 â 2.8 Lactationc 200 4 â 1.6 2.4 aAdapted from Pearson (2005). bDMI = Dry matter intake. cFirst 3 months. TABLE 13-4 Estimated Nutrient Intakes for Adult Donkeys Consuming Diets Based on Poor or Good Quality Forage (dry matter basis) BWa DMI DE Protein Calcium Phosphorus Forage Quality kg kgb Mcal/d kcal/kg BW g g g Goodc 100 2.5 5.15 51.5 270 12.5 7.25 200 5.0 10.30 51.5 540 25.0 14.50 Poor d 100 2.5 4.71 47.1 168 7.60 6.05 200 5.0 9.43 47.1 336 15.2 12.1 aBW = Body weights of mature idle donkeys. bDMI = Dry matter intake, Donkeys fed a good-forage quality, 100 percent of the diet is comprised by forage; donkeys fed a poor-quality forage received 90 percent of the diet as forage and 10 percent as concentrate. cGood-quality forage: Timothy hay (early bloom), DE (Digestible energy): 2.1 Mcal/kg, Crude protein: 10.8 percent, Calcium: 0.51 percent, and Phosphorus: 0.29 percent (Dry matter basis). dPoor-quality forage: Brome hay (mature), DE (Digestible energy): 1.7 Mcal/kg, Crude protein: 6 percent, Calcium: 0.26 percent, and Phosphorus: 0.22 percent (Dry matter basis). The composition of the concentrate used to estimate nutrient intakes (e.g., poor-forage-quality diet) is given in Table 14-1.
274 NUTRIENT REQUIREMENTS OF HORSES ing their energy requirements. Furthermore, protein intake range of dietary crude protein between 12â14 percent. The based on the recommended DMI values by Pearson (2005) latter can be achieved by offering a diet (DM basis) of a and the composition data indicated in Table 13-4 also show 25â40 percent low-protein pellet plus 60â75 percent of higher values than recommended levels. A daily protein in- grass hay (Lintzenich and Ward, 1997). Maintenance re- take of 133 g/d was adequate to maintain miniature donkeys quirements of wild equids are easily achieved on a high- weighing an average of 111 kg BW (Schlegel et al., 2004). fiber diet consisting of free-choice grass hay (10â12 per- Applying the equation for determining the crude protein re- cent crude protein) plus a balanced pelleted feed (12 quirements for a horse under maintenance conditions (BW Ã percent crude protein) fed at a rate of 1 percent of BW per 1.26 g/kg BW/d, see Chapter 4, Protein and Amino Acids), day (Reindl, 1997). Zoos will feed a variety of diets to wild the crude protein requirements will be 126 and 252 g, for horses depending on the institution or geographical loca- 100 or 200 kg BW, respectively. Thus, the calculated values tion. Practical diets for wild equids fed in zoological insti- based on the information given on the above tables should tutions were reported by Schlegel et al. (2004). The crude be taken with caution. protein, ADF, and DE content for these diets ranged be- tween 9 and 15 percent, 30 and 35 percent, and 2 and 2.8 kcal/g, respectively. The proportion of hay fed ranged be- FEEDING MANAGEMENT OF WILD EQUIDS IN tween 50 and 92 percent of the total diet DM and the pellet CAPTIVITY between 7.5 and 51 percent of the diet DM (Table 13-6). The family Equidae is comprised of some eight wild Applying the formula (DE = 1.4 + 0.03 Ã BW) to esti- species within the genus Equus. International Species In- mate DE (Mcal/d) for maintenance requirements in domes- ventory Systems (ISIS, 2002) lists eight wild species of tic horses (Pagan and Hintz, 1986a), all zoo diets showed av- horses with several subspecies (Table 13-5). erage energy levels above requirements (Table 13-6). The Like their domestic relatives, wild equids are bulk- DE maintenance requirements for wild horses at the Zoo- feeding grazers. The anatomy and physiology of the wild logical Society of San Diego and Disneyâs Animal Kingdom horse species have not received special attention and are were calculated to be 9.92 and 10.43 Mcal/d, respectively. presumed similar to that of domestic horses and asses (Nel- The calculated DE maintenance requirements for Toronto son, 1986). In captive environments, wild horses do not Zooâs Przewalskiâs horses and Grevyâs zebras were 10.2 and have special feeding requirements, and the domestic horse 12.4 Mcal/d, respectively. With the exception of diet C, is used as a model to determine nutritional requirements. crude protein content was also above NRC requirements for Many zoological institutions will feed wild equids good- maintenance (NRC, 1989). However, diets in Table 13-6 quality grass hay in the summer and mixed hay in the win- represent offered amounts and not necessarily consumed ter. Ad libitum access to trace mineral block salts is offered. amounts. The Nutrition Advisory Group of the American Zoo and Because obesity is a problem in captive equids, many in- Aquarium Association (AZA) proposed general dietary nu- stitutions will not offer concentrate feeds. Furthermore, re- trient concentrations for feeding zebras and other ungulates cent reports indicated that protein, calcium, phosphorus, in captivity. The recommendations are based on the Na- magnesium, and potassium were fed in excessive amounts to tional Research Council requirements for domestic horses Grevyâs zebras (NRC, 2004) based on the NRC (1989) rec- (NRC, 1989). The authors suggest offering a diet with a ommendations. TABLE 13-5 Wild Equids Found in Zoological Parksa Latin Name Common Name Occurrence Equus przewalskib Przewalskiâs or Asian wild horse In the wild presumably extinct. Reintroduced in Mongolia in the 1990s. Equus quagga Plains zebras, Common or Burchellâs Most commonly found. Certain subspecies are rare. (Six subspecies) Equus zebra Mountain zebra Extremely endangered (Hartmanâs) Equus grevyi Grevyâs zebra Endangered Equus africanus African wild ass Highly endangered Equus onager c Onager (two subspecies) Endangered Equus kiang c Kiang Not threatened Equus hemionus Asiatic wild ass (Kulan, Khur) Extremely endangered aReindl(1997). bAverage body weight: Equus przewalski: 350 kg, Equus quagga: 300 kg, Equus zebra: 320 kg, Equus grevyi: 450 kg, Equus africanus: 275 kg, Equus hemoniuos: 290 kg (Klingel, 1989). cAverage body weight: Equus onager: 254 kg (female), Equus kiang: 275 kg (female), 255 kg (male) (Edwards, 2004).
DONKEYS AND OTHER EQUIDS 275 TABLE 13-6 Diet Ingredients and Nutrient Composition for the first 24 hours of nursing. A common formula used to (dry matter basis) of Typical Diets Fed to Wild Equids in hand-rear many species of wild horses consists of commer- Zoological Parksa cial, fresh, nonfat, and 1 percent low-fat cowâs milk, pow- Nutrient A B C dered edible-grade lactose, and tap water in a ratio of 9:9:1:3 (Blakeslee and Zuba, 2002). The authors recommended Estimated dry matter % 90.0 86.4 90.6 seven feedings per day, as foals do not need to be fed around Crude protein % 15.2 12.5 9.5 Crude fat % 2.9 3.0 1.9 the clock. The daily amount of formula offered is based on ADF % 29.7 31.7 33.2 body weight beginning at 10 percent, divided equally among NDF % 49.3 60.1 60.4 the seven feedings. The amount of formula offered is as- NFC % 36.3 â â sessed every day and increased gradually to account for Ash % 6.98 6.46 6.83 daily weight gains and appetite until the foal is consuming Horse DE Mcal/kg 2.77 2.33 2.10 Mcal/d 15.0 16.5 16.7 16â18 percent of its body weight (around 2 weeks of age). Calcium % 1.09 0.70 0.40 Stomach capacity should be taken into consideration during Phosphorus % 0.51 0.40 0.30 feeding, and foals should be fed no more than 80 percent of Potassium % 1.69 1.59 2.00 their stomach capacity (Blakeslee and Zuba, 2002). After 3 Magnesium % 0.32 0.20 0.15 weeks of age, the foalâs appetite may dictate decreasing the Vitamin E IU/kg 170.0 34.0 28.0 percentage of daily intake to approximately 11â14 percent aDiet A: Zoological Society of San Diego (ZSSD) typical diet offered to a of its body weight, assuming its weight remains constant. variety of wild horses including Eastern kiang, Somali wild ass, Przewal- Weight gains should be constantly monitored. At approxi- skiâs horse, Persian onager, Damara zebra, Grevyâs zebra, and Hartmannâs Mountain zebra (Edwards, 2004); Diet B: Toronto Zoo (TZ) diet offered to mately 4 weeks of age, the feeding frequency should be re- Przewalskiâs horse and Grevyâs zebra (Schlegel et al., 2004); Diet C: Dis- duced to five per day, four times per day at 2 months, and neyâs Animal Kingdom (DAK) diet offered to Grantâs zebra (Schlegel et al., three times per day at 3 months of age, continuing until 2004). The animals on diet C have free access to pastures. Average body weaning. Formula increases are discontinued around 2 weight (BW) for ZSSD horses across species (n = 43) was 284 Â± 33 kg. Av- months of age, when the foal starts eating solids. Wild erage body weight for TZ Przewalskiâs horses (n = 6) was 293 Â± 38 kg and for Grevyâs zebra (n = 3) 367 Â± 29 kg. Average body weight for DAK com- equids may be weaned as early as 4 or 5 months of age. mon zebras (n = 6) was 301 Â± 26 kg. Pelleted feed: Diet A: pellet approx- Early studies by Schryver et al. (1986) showed that milk imately 25% ADF, 14% crude protein; Diet B: pellet approximately 22% from the Przewalskiâs horse, Hartmannâs zebra, and domes- ADF, 30% NDF, 14% crude protein; Diet C: pellet approximately 32% tic horse had similar mineral composition. The authors re- ADF, 50% NDF, 16.4% crude protein, 52% horse total digestible nutrients, ported that the milk of equids taken as a group had certain 2.32 kcal/g horse digestible energy, 5.6% starch. Carrots and/or apples not included on the percentage of the total diet. Diet A: offered approximately similarities such as a low content of total solids. 2% (as fed) of total diet; Diet B: offered at 3.5% (as fed) of total diet; Diet C: offered at 0.4% (as fed) of total diet. NUTRITIONAL DISORDERS IN WILD EQUIDS The wild horse, being similar in anatomy and physiology to the domestic horse, might show similar medical nutri- Preliminary studies reported by Hintz et al. (1976) tional related problems. showed that onagers (Equus hemionus onager) digested dry matter, crude protein, and cellulose from a pelleted diet Colic more efficiently than the Przewalskiâs horse (Equus prze- walski) and Grevyâs zebra (Equus grevyi). Colic in captive wild horses is not as common as in the Studies conducted in zoological institutions showed that domestic horse and is normally associated with sand im- wild captive zebras and other wild hindgut fermenters con- paction. Sand colic is best managed by providing concrete sumed more organic matter per unit time than wild rumi- pads around feeding areas (Walzer, 2003). nants. The higher rates of food intake compensate for their lesser ability to digest plant material. The differences were Enterolithiasis greater for grass than for alfalfa-hay diets (Foose, 1982; Duncan et al., 1990). Consequently, compared to wild rumi- Domestic equids in the western and southwestern United nants of the same size, wild equids extract more nutrients States appear more likely to develop enteroliths than horses per day from a whole range of forages (Table 13-7). in other regions (Lloyd et al., 1987). This might also be true for wild horses. A report by McDuffee et al. (1994) indi- cated the presence of enteroliths in Grantâs zebras; the ele- FEEDING THE YOUNG WILD CAPTIVE EQUID ments forming the enteroliths were primarily magnesium, Orphaned foals of many wild equine species are hand- ammonium, and phosphates, similar to those found in do- reared only if there is maternal neglect or for medical rea- mestic horses. The authors suggested that the higher magne- sons. A newborn should be fed equine or bovine colostrum sium content (5 to 7 times above maintenance requirements
276 NUTRIENT REQUIREMENTS OF HORSES TABLE 13-7 Digestibility Coefficients, Organic Matter (OM) Intake, OM Extraction, and Cell Wall Extraction by Wild Equidsa Grevyâs Mountain Plains Asian Item Zebra Zebra Zebra Wild Ass Timothy Hayb Number of Animals 5 2 4 4 Body weight (kg) 354 272 329 174 Metabolic body weight (W0.75) 82 67 85 50 OM matter digestibility (%) 50 49 48 51 OM intake (g kgâ1W0.75) 101 119 105 104 OM extraction (g kgâ1W0.75) 51 59 51 52 Cell wall digestibility (%) 46 42 45 46 Cell wall intake (g kgâ1W0.75) 73 83 79 63 Cell wall extraction (g kgâ1W0.75) 34 35 36 31 Alfalfa Hayc Number of Animals 2 3 4 3 OM matter digestibility (%) 66 59 62 58 OM intake (g kgâ1W0.75) 104 111 110 127 OM extraction (g kgâ1W0.75) 69 64 68 74 Cell wall digestibility (%) 52 47 45 47 Cell wall intake (g kgâ1W0.75) 49 58 56 70 Cell wall extraction (g kgâ1W0.75) 26 27 25 32 aAdapted from Foose (1982). bPhleum pretense (4â7 percent crude protein; 21â28 percent cell contents; 67â75 percent cell wall). cMedicago sativa (18â22 percent crude protein; 3â60 percent cell contents; 31â56 percent cell wall). according to Lloyd et al., 1987) in California alfalfa fed to Î±-tocopherol values of 4.7 and 6.6 Âµg/ml for foals and adult the zebras might have contributed to the regional prevalence horses, respectively (Dierenfeld et al., 1997). Myodegenera- of enteroliths. Enterolithiasis was observed on necropsy of a tive disorders in zebras (Equus burchelli spp.) caused by Hartmanâs mountain zebra (Decker et al., 1975). The drink- vitamin E deficiency were reported by Wallach (1970). ing water pH may also have an effect on the formation of Equine degenerative myeloencephalopathy (EDM) has been stones. The Zoological Society of San Diego has reported described in many occasions in Przewalskiâs horses, zebras, several cases of enteroliths in captive wild equids that in- and kulans (Walzer, 2003), and vitamin E deficiencies in the cluded 15 cases between 1996 and 2003, predominantly in first year of life have been implicated in the development of kiangs, Somali wild asses, Przewalskiâs horses, a Persian EDM. Foals showing EDM symptoms may be treated with onager, and a Grantâs zebra (Gaffney et al., 1999; Howard et oral vitamin E (1,500â2,000 IU daily: Blythe and Craig, al., 2004). 1997). Single serum Î±-tocopherol values are nondiagnostic for EDM as vitamin E can vary considerably (Walzer, 2003). Early reports on myodegenerative disorders and cardiac my- Vitamin E Deficiency/Myelopathy opathies, as well as impaired reproductive capacity (Blaxter, Degenerative myelopathy has been diagnosed in Prze- 1962; Trinder et al., 1969), have been linked to vitamin E walskiâs horses and related to vitamin E deficiency (Liu et deficiencies. al., 1983). The authors reported mean plasma Î±âtocopherol values in the affected horses of 0.04 Â± 0.01 mg/dl (range: Laminitis < 0.03 â 0.08 mg/dl). Vitamin E values of normal wild horses have been reported by Brush and Anderson (1986). Laminitis occurs rarely in wild equids but, more recently, The authors found mean values of plasma Î±-tocopherol of there have been reports of the disease in Przewalskiâs horses 2.6, 3, and 3.5 Âµmol/L for Przewalskiâs horses (n = 27), on- maintained in semi-natural conditions (Budras et al., 2001). agers (n = 2), and Grantâs and Hartmannâs zebras (n = 5), re- The authors reported that the cause of laminitis in three mares spectively. More recent reports on Przewalskiâs horses in- was the consumption of large amounts of carbohydrate-rich habiting the steppes of Ukraine (n = 19) showed mean feed in the form of rich pasture and under certain climatic
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