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7 Water and Water Quality INTRODUCTION piratory, and cutaneous losses. Lactating mares also lose fluid through milk secretion. Specific physiologic and hus- Water is essential for body fluid balance, digestive func- bandry conditions of the horse, such as lactation and cold tion, and gastrointestinal health. Water, as a universal sol- weather, elicit different water needs. vent, can contribute beneficial and/or detrimental nutrients to the diet of the horse. Horses tolerate water restriction for extended periods, particularly in the absence of feed (Tasker, Fecal Losses 1967a). However, a total lack of water is more rapidly fatal The intestinal tract is the main water reserve for the to horses than a lack of feed. Therefore, health and diet as- horse; consequently, the main route of water loss by the sessments of individual or groups of horses should include horse at maintenance occurs through fluid excreted in feces. evaluation of water criteria, including the quality and vol- Daily fecal water losses by idle, mature horses fed alfalfa ume of imbibed water. hay and pregnant mares fed hay-grain diets ranged from 3–3.8 L fluid/100 kg BW (Tasker, 1967a; Freeman et al., BODY FLUID COMPARTMENTS 1999). Horses fed highly digestible grain-based feeds had drier feces (66 percent moisture) than those fed hay (72–85 Water must be consumed to maintain fluid balance. Total percent) (Cymbaluk, 1989, 1990a; Zeyner et al., 2004). body water (TBW) is partitioned into several main compart- Moist feces (72–85 percent moisture) are common in horses ments: extracellular fluid (ECF), which includes plasma, in- fed all-forage diets, and excretion of fecal water by horses terstitial fluid, transcellular fluid, and lymph, and intracellu- fed hay diets represents 55–63 percent of their daily water lar fluid (ICF). Total body water in adult horses has been intake (Cymbaluk, 1989; Freeman et al., 1999; Warren et al., estimated at 62–68 percent: ECF at 21–25 percent, plasma 1999). Fecal water content and output was positively corre- volume (PV) at 4 percent, and ICF at 36–46 percent of body lated to DM and intake (Cymbaluk, 1989, 1990a). Fecal mass or body weight (BW) (Andrews et al., 1997; Forro et moisture was not only affected by the amount of dietary al. 2000; Fielding et al., 2004). Total body water decreases fiber, but also by the type of fiber. Feces of horses fed diets linearly as horses age (Agabriel et al., 1984). Empty body high in soluble fiber were 5–11 percent wetter than those fed water in foals aged 1, 4, and 8 weeks decreased from 70.6, low-soluble fiber diets (Warren et al., 1999). After 72 hours to 69.1, to 66.2 percent, respectively, concomitant to in- of water deprivation, absolute fecal moisture values de- creases in body fat content (Doreau et al., 1986). Because of creased 7 percent but renormalized within 24 hours of rehy- the higher TBW content, disruption of the fluid supply to dration (Sneddon et al., 1993a). Normal horses deprived of foals creates a more urgent health threat than in adults. water and feed for 8 days decreased fecal output and fecal water excretion to 3 percent of normal output (0.4 L/100 kg BW: Tasker 1967b). Surprisingly, diarrhea occurred after WATER LOSSES several days of water and feed deprivation. Water balance in the horse is achieved by equalizing Clinical abnormalities that impair water reabsorption body water loss with water intake. Water intake occurs di- from the gastrointestinal tract increase water loss through rectly by drinking liquid water and eating moist feed, and in- feces (Tasker, 1967c). Horses with induced diarrhea had directly through metabolism of carbohydrates, protein, and fecal moisture exceeding 90 percent and lost twice the vol- fats. All horses lose fluid by four routes—fecal, urinary, res- ume of water in feces (5.15 mL/kg BWиhr–1 or 12.2 L/100 128

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WATER AND WATER QUALITY 129 kg BWиd–1) than did control horses (Ecke et al., 1998). therefore, fluid losses occur passively through the skin (dif- Plainly, fluid loss by diarrheic horses can greatly exceed fusion) and lungs. Sweating is an active process, involving maintenance water intake. Failure to replenish these fluids secretion of fluid by sweat glands, and is initiated by in- will result in dehydration. creases in body core temperature. Cutaneous fluid losses in horses increased exponentially above ambient temperatures of 20°C (Morgan et al., 1997). In horses participating in Urine Losses long-duration, low-intensity exercise, an estimated 23 per- The kidney regulates body fluid homeostasis in horses. cent of evaporative metabolic heat loss occurs through the When fluid intake greatly exceeds needs, high volumes of respiratory tract, whereas 70 percent or more occurs through dilute urine are produced. Conversely, when water intakes sweating (Kingston et al., 1997). just meet or are below needs, small volumes of concentrated Daily evaporative losses for horses kept in a thermoneu- urine are excreted. With the exception of renal failure, the tral environment were estimated at 10 ± 2.7 L/d with a range kidney continues to produce small amounts of urine even of 1.7–3.3 L/100 kg BW (Groenendyk et al., 1988). The under conditions of total water deprivation. This is the base- hourly evaporative loss by horses housed at temperatures be- line or obligatory urine loss, which in horses was deter- tween –3°C and 20°C was relatively constant at 48 W/m2 mined to be about 0.5 L/100 kg BW (Tasker, 1967c). (71 mL fluid/m2) but exceeded 250 W/m2 (370 mL fluid/m2) Urine volume is typically higher and more variable than at 37°C (Morgan et al., 1997). Based on the equation (qevap = obligatory losses as a result of differences in dietary compo- 48 + 1.02 × 10–4 t4air) derived for evaporative heat loss by the sition, water or fluid availability, and metabolic variations in authors, a 500-kg heat-unadapted horse had an hourly evap- response to changes in ambient temperature, exercise load, or orative heat loss of 0.48 L at 20°C and 1.5 L at temperatures gastrointestinal health. Healthy pregnant mares fed mature 35°C or higher. Daily evaporative losses could total 11.5 L grass hay-grain diets with continuous access to water pro- at temperatures of 20°C or lower, but could exceed 36 L if duced 0.6–0.68 L urine/100 kg BW (Freeman et al., 1999). temperatures of 35°C were sustained. Extended exposure to By comparison, alfalfa-fed nonpregnant horses produced 2.9 temperatures of 35°C or more is uncommon in temperate L urine /100 kg BW (Rumbaugh et al., 1982). In the latter climates, and even if protracted, adaptation is likely within study, when these horses were deprived of feed and water for 2–3 weeks with concomitant reduction in evaporative losses 3 days, their urine output decreased to 1.24 L/100 kg BW (Geor et al., 1996, 2000). after 24 hours, 0.65 L/100 kg BW by 48 hours, and plateaued at 0.63 L/100 kg BW after 72 hours of water deprivation. Ex- Sweat Losses ercise has an unpredictable impact on urine volume. Urine volumes increased in horses performing submaximal exer- Passive cutaneous evaporative loss for idle horses at ther- cise (Hinchcliff et al., 1990), but notably decreased in horses moneutrality (between 5–20°C) is predicted at 6 L/d or less. that were maximally exercised (Schott et al., 1995). Elevated body core temperatures as a result of muscular Urine excretion is dynamic and volume changes can be activity or high ambient temperatures and solar radiation ini- dramatic and immediate in response to variations in nutrient tiate sweating. Total evaporative fluid losses of worked or intake. Donkeys fed wheat straw, then given alfalfa hay, exercised horses depend on duration and intensity of exer- which increased their nitrogen intake by 8-fold, had a quadru- cise, environmental conditions, and acclimation of the horse ple increase in urine flow rates (Izraely et al., 1989). Low di- to its climatic environment. Sweating increased dramatically etary cation-anion difference (DCAD) (85 mEq/kg DM) in- during the first 20–30 minutes of exercise, then plateaued creased urine volume 72–110 percent above moderate (190 thereafter (Kingston et al., 1997). Sweat losses may account mEq/kg DM) and high DCAD (380 mEq/kg DM) (McKen- for 70–92 percent of total evaporative loss by horses during zie et al., 2003). High potassium diets (5.4 mmol potas- exercise (Hodgson et al., 1993; Kingston et al., 1997). Total sium/kg BW) increased urine volume in horses by 26–30 per- body water losses of 20.4 L were reported for horses fol- cent compared to diets that supplied 4.1 mmol potassium/kg lowing a cross-country event (Ecker and Lindinger, 1995) BW (Jansson et al., 1999). A potassium-chloride paste given and body mass losses of 33.8 kg, considered to be largely to dehydrated horses increased their water intake but also in- fluid losses, were recorded in horses performing long-dura- creased urine flow and glomerular filtration rate (Schott et al., tion, low-intensity activity (Kingston et al., 1997). High am- 2002). Thus, any changes to renal solute load, particularly by bient temperatures alone caused evaporative fluid losses to feeding excess protein, sodium, or potassium, can increase quadruple (Morgan et al., 1997), where-as increasing ambi- urine volume and increase water intake. ent temperature from mild (20°C) to hot (35°C) elevated evaporative fluid losses of Standardbred horses by 45 percent (Jansson, 1999). Total Evaporative Fluid Losses Training or conditioning and temperature acclimation in- Heat loss in horses, as in other species, is facilitated crease temperature tolerance and thereby impact water in- through vaporization of water. Evaporative heat losses and, take. Training alone altered the sweating rate of horses, but

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130 NUTRIENT REQUIREMENTS OF HORSES imposing conditions of high humidity and high ambient for Australian stock horses, which were reported to produce temperatures further intensified sweating and respiratory 3.7–3.8 L milk/100 kg BW daily (Martin et al., 1992). Evi- fluid losses (McCutcheon and Geor, 1999, 2000). In cool, dently, milking ability can differ among breeds of mares and dry temperatures (20°C, 50 percent relative humidity [RH]), with mare parity. Based on these data, lactating mares kept Thoroughbreds performing mild exercise lost 1.5 L in thermoneutral environments can be predicted to increase sweat/100 kg BW, which was 82 percent and 73 percent water intake by at least 37–74 percent above maintenance lower than unacclimated horses doing the same exercise in needs solely to meet lactational demands. These water in- hot, dry conditions (34°C, 55 percent RH) or hot, humid creases are only for milk production. Coupled with milk pro- conditions (36°C, 86 percent RH), respectively (Mc- duction, lactating mares also have an increased feed intake Cutcheon and Geor, 2000; Geor et al., 2000). Horses par- which further elevates water demand during lactation (see tially acclimate within 2 weeks of intermittent daily or pro- Pregnancy and Lactation Requirements). longed exposure to temperature extremes, but full acclimation required 3 weeks (Geor et al., 2000). Following WATER INTAKE 3 weeks of acclimation to hot, humid conditions, sweating rates of Thoroughbred horses were 18 percent lower than Horses obtain water by drinking liquid water, from water during initial exposure. Acclimation to the environment, in feed, and from water generated by metabolic breakdown however, does not mean the horse is resistant to dehydration. of dietary carbohydrates, protein, and fat. On pasture, grass Hypohydrated horses, which had lost in excess of 8.5 per- can contribute a substantial amount of water, but in a typical cent of total body water, continued to sweat with continued hay-grain feeding program, the feed and metabolic water exercise (Kingston et al., 1997). This underscores the need contribute little to the daily water requirements of horses. for vigilant monitoring of hydration status of working Metabolic water production by Thoroughbred horses fed horses. hay was estimated at 0.2–0.25 L/hr (van den Berg et al., Dehydration occurs when fluid losses exceed fluid ab- 1998). Daily metabolic water production by Standardbred sorbed. Clinically, signs of dehydration are detected by as- horses fed alfalfa hay in thermoneutral conditions was esti- sessing skin turgor, capillary refill, and heart rate; Collastos mated at 2.9 ± 0.4 L/d or about 0.68 L/100 kg BW (Groe- (1999) described severe dehydration at fluid deficits of 8–10 nendyk et al., 1988). percent. All feeds contain water, but the water content depends on the feed source. Dry feeds such as hay and grain may con- tain 10–15 percent moisture, so in a typical diet these feeds Respiratory Losses contribute only 1–2 L fluid/d (Freeman et al., 1999). Fresh Respiratory heat losses and, consequently, fluid loss forage (pasture), however, can be very high in moisture con- through vaporization accounted for 19–30 percent of the tent and can contribute a large portion of the daily water total heat produced by horses performing mild to intense ex- needs of the horse. A vegetative perennial ryegrass pasture ercise, with absolute fluid losses via the lung of 0.8–2.1 L containing 79.6 percent moisture was reportedly consumed (Hodgson et al., 1993; Kingston et al., 1997). These values in amounts of 61–75 kg by pregnant mares and 39.5 kg by would be likely to increase in warm or tropical environ- nonpregnant mares (Marlow et al., 1983). Although based ments. Acclimation to high heat was accomplished through on a small sample of horses, these data indicate that fresh increased sweating and elevated respiratory rates (Geor et pasture contributed between 31–60 kg fluid, an amount that al., 2000). Fluid losses through the respiratory tract are dif- approaches the mares’ water requirements (Table 7-1). ficult to quantitate. Respiratory heat loss and, therefore, res- piratory fluid loss vary with duration and intensity of the ex- Dietary Effects ercise, ambient temperature, and other environmental conditions imposed during exercise. Diet influences water intake by horses depending on the amount eaten and by the composition of the consumed feed. Total DM intake and composition directly affect the amount Lactational Losses of water consumed by mature ponies and weaned foals During the first 2 months of lactation, primiparous and (Cymbaluk, 1989, 1990b). Horses fed forage diets ate 19 multiparous Quarter horse mares produced about 1.8 and percent more DM to provide a similar caloric intake to 2 L milk/100 kg BW daily, respectively, which declined those fed a mixed diet and, consequently, drank 26 percent thereafter (Pool-Anderson et al., 1994). Earlier studies with more water (Pagan et al., 1998). Likewise, horses fed 5.8 kg Quarter horse mares had reported daily milk volumes up to of a hay-only diet drank 17.8 kg water compared to 10.1 kg 2.1 L/100 kg BW over 150 days (Gibbs et al., 1982). Notably water consumed by horses fed 1.8 kg grain plus 1.3 kg higher daily milk volumes were reported for primiparous and hay (Danielsen et al., 1995), perhaps because of a lower multiparous heavy and light mares, which produced 2.4 and DM intake as well as a different dietary composition. Dur- 2.8 L milk/100 kg BW, respectively (Doreau et al., 1991) and ing transportation, horses greatly reduced their feed intake

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WATER AND WATER QUALITY 131 TABLE 7-1 Estimated Water Needs of Horsesa Water Average Estimated Exercise Diet Intake Body Total Range of Ambient Duration (kg /100 kg BW) (L/100 kg Weight Water Intake Water Intakesb Class Temperature (°C) (hr) Amount Type BW) (kg) (L/d) (L/d) Idle, mature 20 — 1.5 5 500 25 21–29 30 — 1.5 Hay only 9.6 48 42–54 20 — 2.0 6.7 33.5 30–38 Idle, mature 20 — 2.0 Hay-grain 6.2 500 31 27–35 –20 — 2.5 Hay only 8.4 42 37–47 Pregnancy 20 — 2.0 Hay-grain 6.2 500 31 27–35 Lactating 20 — 3.0 Hay only 11.9–13.9 500 65 52–78 20 — 2.5 Hay-grain 9.2–11.2 51 40–63 Moderate exercise 20 1 hr 2.2 Hay-grain 8.2 500 41 36–46 35 (daily average) 1 hr 2.2 16.4 82 72–92 Yearling –10 — 2.0 Hay-grain 6.0 300 18 16–20 20 — 2.0 6.3 19 17–21 aBased on a horse with a mature weight of 500 kg. bValues are averages and specific water intakes by individual horses may be lower or higher depending on the individual horse’s baseline, its clinical health, and variations in environmental conditions. Calculations are based as follows: 1. Maintenance water intake by idle, adult horses is 5 L/100 kg BW when diet is fed at 1.5 kg/100 kg BW. 2. Temperature effects above 20°C (5–20 used as thermoneutral) used the equation of Morgan et al. (1997) to calculate hourly evaporative heat loss (qevap = 48 + 1.02 × 10–4 t4air) where tair is the ambient temperature measured in °C and qevap is measured in W/m2, which is converted to mL water based on the con- version factor of 2,428 J evaporate 1 g (mL) of water. Temperature effects on feed-water intake relationships of yearling horses were based on the equation derived by Cymbaluk (1990b) in which Y = 2.25 + 0.016T (Y = L water/kg DM intake; T = ambient temperature measured in °C). Hence, temperature effects are incorporated into the dietary component for yearlings. 3. Fluid losses in milk were based on published data indicating that milk production ranges from 1.8–3.8 L/100 kg BW. 4. Sweat and respiratory heat losses during exercise were based on Geor et al. (2000) in which horses lost 1.5 L/100 kg BW fluid at thermoneutral tempera- tures and 2.5 L/100 kg BW fluid at temperatures above 30°C. 5. Dietary effects assumed that for each 1 kg/100 kg BW of an all-hay diet eaten above 1.5 kg/100 kg BW, water intake would increase 3.4 L/100 kg BW and would increase 2.4 L/100 kg BW for hay-grain diets. with attendant reductions in water intake (Smith et al., when the predominantly forage diets were fed were attrib- 1996). uted to higher intakes of total fiber (Warren et al., 1999). Although diet affects water intake, the converse is also Water intake has a positive, linear correlation to salt in- true; limiting water intake reduces feed intake. Gradual take (y = 36.5 + 0.22x where y = daily water intake in mL/kg water restriction reduced feeding activity by 4–29 percent BW and x = daily sodium intake in mg/kg BW: Jansson and (Houpt et al., 2000). After 72 hours of total water depriva- Dahlborn, 1999). Yet, salt added to the diet at 1, 3, and 5 per- tion, horses continued to eat concentrate at a near constant cent did not affect water intake or urine volume of horses rate, but hay intake dropped by 45 percent (Sneddon et al., (Schryver et al., 1987). Diets containing 5.4 mmol potas- 1993a). Feed consumption, however, did not decrease until sium k/kg BW/d increased water intake 6.8 percent com- after 48 hours of water deprivation. Ponies and donkeys de- pared to diets containing 4.1 mmol K/kg BW to offset the el- prived of water for 36 hours reduced their feed intake by 32 evated urine output associated with elimination of excess percent and 13 percent, respectively (Mueller and Houpt, potassium (Jansson et al., 1999). 1991). Donkeys were tolerant of water deprivation through water conservation strategies that incurred only modest re- Temperature Effects ductions in feed intake. Dietary composition—notably fiber, protein, and specific Ambient temperatures that fluctuate radically from ther- minerals such as sodium and potassium—can alter water in- moneutrality influence water intake. Cold weather reduced take by the horse, generally through increased urinary ex- water intake by 6–14 percent (Cymbaluk, 1990b). At –8°C cretion. Water:feed ratios for mature ponies fed grass or al- and –17°C, weaned foals drank 2.3 and 2.1 L water/100 kg falfa hay or high-grain complete pellets were 3.2, 3.3, and 2, BW compared to cohorts housed at temperatures above 8°C, respectively (Cymbaluk, 1989). Similarly, water:feed ratios which drank 2.4 L water/100 kg BW. Free water intake was of 3.4, 3.3, and 2.6 were reported for horses fed alfalfa-beet directly related to ambient temperatures in the range of –20 pulp, 77 percent hay-oats, and other forage-grain diets, re- to 20°C by the equation Y = 2.25 + 0.016T where Y = L spectively (Warren et al., 1999). The higher water intakes water/kg DM intake and T = ambient temperature in °C

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132 NUTRIENT REQUIREMENTS OF HORSES (Cymbaluk, 1990b). Compared to water intakes (5.15 L/100 Dahlborn, 1999). Although breed differences in water intake kg BW) during exercise in a thermoneutral environment have not been identified in horses, donkeys appear to drink (20° C and 45– 50 percent RH), daily water intake increased less water then ponies. Donkeys housed and fed similarly to 79 percent when horses were exercised at high temperatures ponies drank 30 percent less water (5 L/100 kg BW) than the (33–35°C) coupled with high humidity (80–85 percent) for ponies (6.5 L/100 kg BW) but also consumed 16 percent 4 hours (Geor et al., 1996). less feed (Mueller and Houpt, 1991). Based on these data, Water temperature influences water intake depending on the estimated maintenance requirement for water by a 500- environmental temperature. Cold weather alone reduces kg horse kept at thermoneutral temperatures fed hay at 1.5 water intake, but horses also drink less cold water than warm kg/100 kg BW ranges from 21–29 L/day. water during cold weather. At 0–5°C, pastured, lactating mares drank infrequently, but as temperatures increased so Suckling Foal Requirements did drinking frequency. During hot weather (30–35°C), mares drank every 1.8 hours (Crowell-Davis et al., 1985). Nursing and orphan foals drink water in addition to the Pony stallions kept outdoors or indoors at cool ambient tem- fluid obtained from the dam’s milk or liquid milk replacer. peratures drank 38–41 percent less near-frozen water than Thus, accessible water should be available to dam and foal water heated to an average temperature of 19°C (Kristula at all times. Pastured, suckling foals drank 3.9 kg of water at and McDonnell, 1994). Yet, pony stallions kept indoors at 1 month of age in addition to suckling 17.4 kg milk and con- warm ambient temperatures (15–29°C) drank similar tinued to increase water intake up to 5.5 kg/d during the next amounts of warm (average 23°C) or icy (0–1°C) water (Mc- month of growth with no concurrent decreases in milk in- Donnell and Kristula, 1996). Horses given a saline solution take (Martin et al., 1992). Orphan foals drank a total of immediately after exercise on a treadmill in a room kept at 14.8–15.9 L fluid (water and liquid milk replacer)/100 kg 25°C at a relative humidity of 60 percent preferred a luke- BW beginning at 1 week of age, which progressively de- warm solution (20°C) to a cool solution (10°C) or warm so- clined to 10.2–10.8 L/100 kg BW by 7 weeks of age as re- lution (30°C) (Butudom et al., 2004). liance on formula decreased and creep feed intake increased (Cymbaluk et al., 1993). MAINTENANCE REQUIREMENTS Pregnancy and Lactation Requirements In typical horse management settings, horses consume most of their daily water needs by drinking liquid water. Pregnancy does not appear to impose increases in water Body weight is the main determinant of the total volume of intakes above maintenance except in response to diet type or water imbibed. Maintenance water intake of adult horses fed imposition of exercise. Pregnant, idle mares kept indoors at a dry diet approaches values of about 5 L/100 kg BW. Free thermoneutral temperatures fed a grass hay-grain diet at 2.2 water intake by normal, nonworking horses fed alfalfa- percent of body weight drank 4.5–5.9 L water/100 kg BW, timothy or alfalfa hay ad libitum was 5.1–5.6 L/100 kg BW irrespective of whether water was provided intermittently or (Tasker, 1967a; Groenendyk et al., 1988). Likewise, water ad libitum (Freeman et al., 1999). Both absolute and weight- intakes of 4.4–4.8 L/100 kg BW were reported for stabled, scaled water intakes declined slightly during pregnancy. grass-fed Namib and Boerperd horses (Sneddon et al., Higher water intakes (6.9 L/100 kg BW) were reported for 1993b). Stabled, mature ponies fed grass or alfalfa hay at pregnant Thoroughbred mares fed hay-only diets (Houpt et maintenance rates drank 5–5.5 L water/100 kg BW/d (Cym- al., 2000). Total daily water intakes by pregnant mares baluk, 1989). Average maintenance water intakes are about weighing 500 kg depend in part on diet but are expected to 5 L/100 kg BW/d, but individual horses of similar weight be in the range of 27–38 L. fed similar diets can have very different water intakes. Not Few water intake data are available for lactating mares, only are differences evident among horses, but also the same but water intakes may increase significantly above mainte- individual has very different day-to-day water intakes nance and pregnancy because mares lose additional fluid (Groenendyk et al., 1988). Absolute water intake by preg- through lactation and eat considerably more feed to sustain nant mares fed identical diets varied by 16–20 percent and milk production (Doreau et al., 1992). Dry matter intake by weight-scaled water intake varied by 11–13 percent from the draft mares after 2 weeks lactation exceeded 3 kg DM/100 average (Freeman et al., 1999). Similarly, individual Stan- kg BW whether the mares were fed a high-forage or high- dardbred horses had absolute water intakes that deviated concentrate diet (Doreau et al., 1992). Adult horses typically 21–25 percent from the average (Nyman et al., 2002), ate 2 kg DM/100 kg BW (Dulphy et al., 1997) and pregnant whereas Thoroughbred mares had weight-scaled water in- mares ate 1.7–1.8 kg DM/100 kg BW (Doreau et al., 1991). takes that varied 64 percent (Smith et al., 1996). Daily vari- Consequently, water intake by lactating mares would be ex- ation in water intake by the same horse has been attributed pected to increase by 50–75 percent to compensate for a to variation in voluntary DM intake or variation in intake of higher feed intake. Coupled with an increase of 37–74 per- other dietary components such as salt (Jansson and cent in water intake to offset milk secretion, lactating mares

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WATER AND WATER QUALITY 133 would be expected to drink 1.8–2.5-fold more water than creased (Smith et al., 1996). Horses transported for longer consumed at maintenance in thermoneutral conditions. Total than 30 hours without water became unfit for further trans- water intakes will vary with diet and ambient temperature port, whereas those given water were able to tolerate an ad- but volumes of 40–78 L/d are predicted for a 500-kg lactat- ditional 2 hours of transportation (Friend, 2000). ing mare, or approximately 2- to 3-fold greater than at main- tenance. DRINKING BEHAVIOR OF HORSES Water consumption by horses is episodic and circadian. Work or Exercise Requirements Drinking patterns are modified by water source, water avail- Water needs of working or competitive horses are diffi- ability, and age of the horse. Each drinking episode is bipha- cult to predict. Water loss and water intake depend on envi- sic: a long single draught is followed by sips of shorter du- ronmental conditions (mainly ambient temperature, humid- ration. Normal drinking behavior for housed, adult horses ity, and solar radiation), duration and intensity of the work, has the following characteristics: episodes occur 2–8 times and fitness and acclimation of the horse to specific environ- per day and last 10–60 seconds per episode with a cumula- mental conditions. Light activity causes only marginal in- tive daily total drinking duration of 1–8 minutes (McDon- creases in water intake. Lightly trained horses drank 24 L nell et al., 1999). The number of drinking bouts reported for water by bucket or 17 L from an automatic water bowl horses watered through pressure-valve water bowls, float- (Nyman et al., 2002), which are within a maintenance range. valve water bowls, and buckets ranged from 16–21 episodes However, in actual performance, fluid losses can be exten- daily with drinking durations of 10–52 seconds per episode sive depending on exercise duration and intensity and envi- (Nyman and Dahlborn, 2001). In the first 5 minutes after ex- ronmental conditions. Body weight losses of Arabian horses ercise, horses had 6, 10, and 11 drinking episodes when after an 80- or 160-km endurance ride averaged 15 ± 2.2 kg, saline was offered at temperatures of 10, 20, and 30°C, re- with a maximum loss of 28.2 kg (Schott et al., 1997). spectively (Butudom et al., 2004). During the subsequent Weight losses were considered to be largely fluid and repre- hour of recovery, drinking episodes of water decreased sented losses of 3.6–7.7 percent of BW. To calculate water (4–4.6) and were unaffected by temperature of the offered needs of exercised horses, both weather conditions and ex- water. ercise load must be considered. In hot weather, unexercised The duration of a drinking episode by horses is brief. horses sustained hourly sweat losses of 1.5 L/100 kg BW. In Suckling foals spent little total time drinking water and hot, humid conditions, horses performing submaximal exer- drinking bouts were short, only lasting 0.34 ± 0.06 minutes cise lost fluid through sweat at rates of 2–2.5 L/100 kg (Crowell-Davis et al., 1985). The daily frequency of drink- BWиhr–1 compared to 1.5 L/100 kg BWиhr–1 in cool, dry en- ing episodes by pregnant mares fed dry feed and housed in- vironments (Geor et al., 2000). Based on these data, water doors ranged from 18–39 times and each drinking episode intake by exercised horses can increase 2- to 3-fold over lasted from 0.22–0.44 minutes (McDonnell et al., 1999). maintenance depending on the duration and conditions of Drinking bouts by lactating mares on pasture were remark- exercise. Total water intakes by a 500-kg horse could range ably similar, lasting 0.39 ± 0.02 minutes (Crowell-Davis et from 36–92 L per day depending on conditions of exercise al., 1985). Drinking bouts by bucket-watered pony geldings (Table 7-1). lasted 12.2–24.2 seconds (Sweeting and Houpt, 1987), sim- For most forms of horse activity, liquid water is sufficient ilar to mean values of 11–28 seconds observed for group- to offset fluid losses. Special considerations are needed for transported horses (Gibbs and Friend, 2000). Thus, the total horses involved in intense physical work or exercise, espe- time during the day a horse spends drinking is remarkably cially when exercise is performed in hot, humid, sunny con- small. Pregnant heavy and light mares with ad libitum ac- ditions. Water, although certainly the most available fluid cess to water drank for 6.2 min/d compared to 5.7–10.7 source, may not be the preferred fluid of choice during ex- min/d when offered water at regular intervals using a float- ercise or during recovery of the work-exhausted horse. type water bowl (McDonnell et al., 1999; Flannigan, 2001). Compared to giving no fluid during exercise, providing Likewise, Standardbred geldings spent a total daily drinking water or electrolyte solution was beneficial in reducing the time of 3–15 minutes irrespective of whether the water was extent of the fluid loss but neither solution prevented hypo- supplied in buckets or by water bowls equipped with either hydration (Geor and McCutcheon, 1998). In all cases, the a float valve or pressure valve (Nyman and Dahlborn, 2001). choice of fluid for rehydrating exhausted horses should al- Longer daily drinking times (21–27 min/d) were reported ways be made in conjunction with a clinician. for ponies fed and watered ad libitum (Sufit et al., 1985). Transportation of horses creates its own unique water The type of water bowl and watering method can influ- drinking requirements and behaviors. Horses that were of- ence duration of drinking and volume of water consumed. fered water during transport showed a diurnal water intake Bowls holding water 2.5–5 cm deep appeared to increase the pattern consuming less water during the cool periods of the drinking duration of horses, because the depth may have re- day. During transportation, both water and feed intake de- stricted the horse’s ability to ingest water quickly (McDon-

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134 NUTRIENT REQUIREMENTS OF HORSES nell et al., 1999). In a preference test comparing water bowls directly or indirectly. Water source and availability can be to buckets, horses favored drinking from buckets and drank readily assessed. Direct measure of water intake is the sim- 98 percent of their daily intake from buckets and only 2 per- plest and most reliable way to measure volume of water cent from a pressure-valve bowl or a float-valve bowl drunk by the horse. Water intakes are easily attained for (Nyman and Dahlborn, 2001). As seen with shallow water bucket-watered horses. Simple water meters can be grafted bowls (McDonnell et al., 1999), horses spent more time into water lines of automatic watering systems. Water intakes drinking from the pressure-valve waterer but consumed less are recorded over a period of days, and then daily water in- water than when water was supplied by bucket or float wa- takes can be interpreted as appropriate for the horse’s weight, terers (Nyman et al., 2002). diet, function, and ambient housing temperature. Horses drink when they eat (Sufit et al., 1985; McDon- Water can be provided in various ways. The simplest nell et al., 1999; Nyman and Dahlborn, 2001). Drinking was guideline for watering horses is to provide fresh, clean water periprandial (less than 2 hours after eating) for 75–89 per- at all times, but often this is neither possible nor hygienic. cent of the drinking episodes observed in ponies fed ad libi- Obvious limitations exist where horses graze on extensive tum and horses fed four times daily (Sufit et al., 1985; pastures and must walk considerable distances to get to Nyman and Dahlborn, 2001). Prandial drinking was felt to water, or in unheated riding stables where cold temperatures occur as a response to an increased plasma osmolality or freeze water lines, thereby precluding use of automatic wa- total serum protein associated with the consumption of feed tering systems. Intermittent provision of water in voluntary (Sufit et al., 1985; Pagan and Harris, 1999). Water intake rel- amounts supplied horses with their maintenance water needs ative to the time of grain feeding was significantly altered (Freeman et al., 1999), so the use of buckets for watering as when hay was fed at the same time, 2 hours before or 4 appears to be the practice in many horse barns is acceptable hours after feeding grain (Pagan and Harris, 1999). How- as long as sufficient water is provided. Buckets are still ever, peak water intakes fell within the 2-hour periprandial commonly used in horse husbandry and are not only pre- period of hay feeding. By contrast, daily water intake pat- ferred by horses (Nyman et al., 1997) but, along with bulk terns of Standardbred horses offered similar amounts of hay- water tanks and automatic waterers, are associated with sig- oats diets either two or six times per day did not differ (Jans- nificantly lower risks of colic (Kaneene et al., 1997). son and Dahlborn, 1999). Total water intake was unaffected by feeding frequency, but water consumed at each feeding WATER QUALITY FOR HORSES period was not uniform through the day. Horses drank more water in the afternoon and evening than in the morning Water quality refers to both the suitable and unsuitable (Jansson and Dahlborn, 1999). Pastured, lactating mares characteristics of water that determine whether it is accept- drank 86.4 percent of their daily water intake between 9:00 able for a specific purpose or use. Acceptable water stan- am and 9:00 pm (Crowell-Davis, 1985). dards may vary regionally, nationally, and internationally. Stall-housed horses are commonly observed to dip hay or The upper limits and acceptable concentrations of sub- wet hay in the manger (McDonnell et al., 1999). Although stances in water that are currently used in the United States hay dipping and unlimited access to water can create hy- are largely based on the summary of data described by an giene problems in mangers (Freeman et al., 1999), this be- NRC (1974) document. Individual states may or may not havior was felt to be a normal way to moisten dry feed to have updated livestock water quality criteria since that pub- make it more palatable and easier to masticate (McDonnell lication. Many water quality criteria can be cross-referenced et al., 1999). at the extensive database available through the USDA Co- The behavioral manifestations of water restriction are operative State Research, Education, and Extension Service less dramatic than those of horses totally deprived of water. (CSREES) National Water Quality Network (http://www. In water-restricted horses, the only behavioral changes usawaterquality.org) and the United States Geological Sur- recorded were a reduction in time spent eating and an in- vey (http://waterdata.usgs.gov/nwis/). Maximum acceptable crease in time spent mouthing the watering buckets (Houpt concentrations, interim acceptable concentrations, and aes- et al., 2000). Horses deprived of water for 8 days showed re- thetic objectives of chemical components for livestock were markably few behavioral changes except a loss of skin tur- recently updated for Australia and New Zealand (ANZECC, gor and a tucked-up appearance (Tasker, 1967c). 2000) and Canada (CCME, 2002). A vast body of water re- search has been accumulated since the NRC publication in 1974, yet water quality data for livestock consumption ap- WATER MANAGEMENT pear to have received less attention than water contamina- Regardless of how water intake measurements are made, tion by livestock. The absence of controlled studies on water interpretation of adequacy of water intake must integrate in- quality for horses makes it necessary to adapt water quality formation related to BW, age, diet, exercise intensity and du- standards for horses from safety indexes used for other do- ration, lactation needs, ambient temperature, and gastroin- mestic livestock or for humans. testinal health. Adequacy of water intake can be evaluated

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WATER AND WATER QUALITY 135 Horses do not drink pure water. Horses drink ground often based on TDS or total soluble salts (TSS) (Table 7-2). (deep or shallow aquifers) and surface water (streams, lakes, TDS is a measure of the aggregate composition of the ions ponds, dugouts, and sloughs), which acquires all the aspects in the water but does not discern the type of ions present— of the geochemistry, runoff, evaporation, precipitation, only the concentration of ions present in the water sample. farming practices, and human and animal activity in its sur- Depending on type of ion present, water may or may not be roundings. Because of these numerous influences, water palatable. Water has been described in terms of TDS con- characteristics from wells and surface waters are constantly centrations. A TDS of less than 1,500 mg/L indicates fresh changing. Thus, a single water analysis is not representative water, 1,500–5,000 mg/L indicates brackish water, 5,000– of the chemical attributes of the water ingested by the horse 30,000 mg/L is saline water, 30,000–100,000 mg/L is sea- throughout the year. water, and greater than 100,000 mg/L is brine (NRC, 1974). Ground water is a source of free water whose water com- Typically, surface water has a lower TDS than groundwater. position can be altered by dissolution, precipitation, ion ex- Australian and New Zealand livestock quality guidelines change, or reduction or oxidation of compounds percolating (ANZECC, 2000) suggest that water with a TDS of 0–4,000 through soil and rock. A near linear relationship exists be- mg/L causes no adverse effects in horses, water with tween mineralization and the depth of the ground water. Gen- 4,000–6,000 mg/L TDS might affect initial intake until erally, the principal anion in shallow wells is bicarbonate, fol- adaptation occurs, but waters with greater than 6,000 mg/L lowed by sulphate in deeper wells, while chlorides dominate may affect health and productivity. These guidelines, how- in the deepest wells. Calcium is the major cation in water of ever, were not confirmed with studies using horses. Gener- shallow wells, followed by magnesium then transitioning to ally, TDS is low (< 350 mg/L) in waters found on both sodium in deeper wells. These are generalizations: specific coasts of North America. High TDS (> 2,500 mg/L) are wells may have quite different cation and anion distributions. found only in small areas of Texas (NRC, 1974). Hardness is the total cationic effect of calcium and mag- nesium in water. Past methods of analysis equated hardness Physical Criteria with calcium carbonate equivalents. Water quality in terms Physical criteria used to describe water quality are tur- of hardness is given in Table 7-3. Calcium, magnesium, and bidity, total dissolved solids (TDS), odor, color, and temper- sodium are mainly derived from mineral deposits, and ature. Turbidity assesses water clarity but is a seldom-used potassium from soil organic matter. A detailed description of criterion. Turbidity in water may increase significantly after the mineral sources associated with specific water cations extreme rainfall and runoff events (Kistemann et al., 2002). has been described (NRC, 2005). For example, water cal- Odor may affect water palatability for horses, but this is not cium is typically associated with carbonate, gypsum, a test frequently conducted on livestock water. Distinctive feldspar, pyroxene, and amfibole. Hard water typically con- odors in water are attributed to sulfates, tannins, manure, tains high concentrations of calcium and magnesium. How- rotting vegetation, and algal and microbial byproducts ever, neither water calcium nor magnesium is felt to con- (Hargesheimer and Watson, 1996). There are no controlled tribute significant amounts to the dietary balance of these studies to assess the impact of odoriferous water on intake minerals to the horse. by horses, but clean water may be important. Transported The pH of water shows the hydrogen ion concentration horses drank notably less water from a trough contaminated and is an indication of the reactivity of the water with other with feces (Friend, 2000). Color does not usually affect dissolved compounds in the water and with containers. The water quality or horse health but can affect human percep- most important anions in water that contribute to alkalinity tion of quality for their horses. Pigments that give color to water can originate from suspended soil particles, tannins arising from organic matter, or iron-fixing bacteria. The lat- ter are not uncommon in inconsistently cleaned water bowls. TABLE 7-2 Guidelines for Total Dissolved Solids (TDS) Temperature not only affects the palatability of water for or Total Soluble Salts (TSS)a horses, but also it can affect growth of bacteria and certain < 1,000 Safe and should pose no health problems algae. At cool ambient temperature, horses drank 34–41 per- 1,000–2,999 Generally safe but may cause a mild temporary diar- cent less icy water than warm water (Kristula and McDon- rhea in unaccustomed animals nell, 1994), but when ambient temperatures were warm, 3,000–4,999 Water may be refused when first offered to animals or their intakes did not differ between icy or warm water (Mc- may cause temporary diarrhea. Animal performance Donnell and Kristula, 1996). may be less than optimum because water intake is not optimized 5,000–6,999 Avoid these waters for pregnant or lactating animals. Chemical Criteria 7,000 This water should not be offered. Health problems or Water quality is most commonly associated with its poor production may occur. chemical characteristics. For livestock, water suitability is aSOURCE: NRC (1974).

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136 NUTRIENT REQUIREMENTS OF HORSES TABLE 7-3 Water Hardness Guidelinesa carbonate determine the pH and “alkalinity” of water. Chlo- ride waters occur throughout the world, while sulphate wa- Descriptor Hardness (mg/L) ters occur in central and western North America. Chloride Soft 0–60 content is used to evaluate wastewater usability for agricul- Moderately hard 61–120 tural purposes. Hard 121–180 Very hard > 180 Sulphate in water is important in ruminants, especially aSOURCE: if feed molybdenum is high, because the copper- NRC (1974). thiomolybdate complex that forms reduces copper availabil- ity (Spears, 2003). To date, there is no evidence that high sulphate water impairs copper utilization in horses. High are carbonate, bicarbonate, and hydroxyl ions. The acidity sulphate concentrations in water may cause metal corrosion. or alkalinity of the water will also determine the biota that A “salty” taste may be detected typically due to the sodium, will survive therein. For example, pH values of 5–9 are ac- the cation most commonly associated with sulphate. cepted for domestic water, and values of 6.5–8.5 are accept- Although few studies have examined individual cation able for marine and freshwater aquatic life. and anion toxicities in horses, Table 7-4 provides an esti- The cationic elements in water that affect its quality de- mate of generally considered safe upper level concentrations pend directly on the area and its constituent geological of some potentially toxic elements for horses. This summary bedrock and soils (McLeese et al., 1991; Betcher et al., is an amalgam of past and more recent livestock water 1995). Sodium tends to dominate in saline lakes, alkali guidelines. The data have generally not been derived from lakes, and ground sources. In alkali areas of the Canadian studies using horses. Prairies, sodium content of water in pig barns averaged as high as 258 mg/L with a range of 4–1,390 mg/L (McLeese Nitrate et al., 1991). Two unconventional sources of sodium con- tamination of water are water softening agents and road de- High water nitrate and nitrite concentrations are a concern icing salt. In rural and urban locations, cation exchange for humans, particularly infants and the elderly (Fan and water softeners often use sodium chloride to reduce water Steinberg, 1996). The upper limit for nitrate-nitrogen in water hardness. Softened household water contained 278 ± 186 for livestock has been specified at 100 mg/L and for nitrite- mg sodium/L (range 46–1219 mg/L) compared to untreated nitrogen at 10 mg/L (NRC, 1974; CCME, 2002). Australian municipal water, which had 110 ± 98 mg sodium/L (range water guidelines use trigger values of 400 mg nitrate/L and 30 0–253 mg/L) (Yarows et al., 1997). The second unusual mg nitrite/L (ANZECC, 2000) or about 90 mg/L nitrate- source of extraneous water sodium occurs in northern geo- nitrogen and 9 mg/L nitrite-nitrogen. Nitrate and nitrite con- graphical areas, which use de-icing salt to melt roadway ice centrations in water analyses are converted to their respective in winter. During the spring thaw, residues of de-icing salt in nitrogen values (nitrate-nitrogen and nitrite-nitrogen) by di- ditch water have been shown to contaminate waterways not viding by 4.43 and 3.29. Of the two components, nitrite is only with sodium, but also with other heavy metals includ- 10–15 times more toxic than nitrate. Nitrate, however, can be ing cadmium, copper, lead, and zinc (Backstrom et al., converted to nitrite by bacterial reduction in the rumen of cat- 2004). tle or sheep and to a lesser extent in the cecum of the horse. A water sodium concentration of about 350 mg/L will Nitrite creates its toxic effects by displacing oxygen on the provide sufficient sodium to meet the daily sodium require- hemoglobin molecule to form methemoglobin. Methemoglo- ments of a horse drinking maintenance amounts of water bin reduces oxygen transport to tissue, which results in the (5 L/100 kg BW). The upper limits of sodium concentra- typical respiratory symptoms of nitrite (nitrate) poisoning. tions (1,390 mg/L) detected in some Prairie waters Few cases of nitrite- or nitrate-induced methemoglobinemia (McLeese et al., 1991) would provide four times the sodium in horses are reported in the literature. A recent report in needed by an idle horse. In other livestock, high water which diets containing 1.74–1.85 percent nitrate were fed to sodium may reduce the palatability and voluntary intake of nonpregnant mares observed that neither methemoglobin, the water and may be a potential cause of dehydration. High oxygenated haemoglobin, reduced haemoglobin, or hemat- sodium content in water has implications regarding volun- ocrit were significantly changed after 13 days of feeding de- tary intake of block or loose salt and/or water by horses. A spite significant elevations in blood nitrate/nitrite concentra- decreased salt intake could impact horse health if salt is the tions (Burwash et al., 2005). This suggests that horses may only mechanism of providing trace minerals to the horse. have a different threshold of nitrate and nitrite tolerance than The sodium content of the regional water supply should be ruminants. Generally, feed nitrate is a larger risk than water considered during ration formulation. nitrate, but the cumulative effects of high feed and water ni- Bicarbonate, carbonate, sulphate, and chloride are the trate (nitrite) intakes should be avoided. principal anions in water. Bicarbonate (carbonate) water is The nitrate concentration of water has been described in common in Africa and western Canada. Carbonate and bi- a multivariable relationship with the following significant

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WATER AND WATER QUALITY 137 TABLE 7-4 Generally Considered Safe Upper Level Concentrations (mg/L) of Some Potentially Toxic Nutrients and Contaminants in Water for Horses Livestock Livestock Upper Upper Water Water Limit Limit Guidelines Guidelines Element (NRC, 1974) (NRC, 1989) (ANZECC, 2000) (CCME, 2002) Aluminum — — 5 5 Arsenic 0.2 0.2 0.5 0.025 Boron — — 5 5 Cadmium 0.05 0.05 0.01 0.08 Chromium 1 1 — 0.05 Cobalt 1 1 — 1 Copper 0.5 0.5 0.5–5a 0.5–5a Fluoride 2 2 2 1–2 Lead 0.1 0.1 0.1 0.1 Mercury 0.01 0.01 0.002 0.03 Molybdenum Not established 0.15 0.5 Nickel 1 1 1 1 Selenium — — 0.02 0.05 Vanadium 0.1 0.1 — 0.1 Zinc 25 25 20 50 aLower limits for sheep and cattle; higher values for pigs and poultry. factors: nitrogen fertilizer loading, extent of cropland or pas- al., 1997; Rose, 1997; Sturdee et al., 2003) in which diarrhea ture, human population density, well-drained soils, depth to is the most common clinical sign. In North America, an av- the seasonally high water table, and presence or absence of erage prevalence of infection with Cryptosporidium in unconsolidated sand and gravel aquifers (Nolan et al., horses is 16 percent, 50 percent in dairy calves, and 78 per- 2002). Manure and agricultural fertilizers are usually felt to cent in sheep (Rose, 1997). Cryptosporidium oocyst num- be the main sources of nitrate in water. In agricultural coun- bers in feces of British horses varied annually, but the aver- ties of upstate New York, 10 percent of small farms (100 age prevalence rate was 8.9 percent (Sturdee et al., 2003). acres or less) and 23 percent of large farms (501 acres or The prevalence of infection in horses with Giardia and more) had water nitrate exceeding 10 mg/L (Gelberg et al., Cryptosporidium in west-central Canada and the Yukon was 1999). Wells less than 15 meters deep, and springs located 20 percent and 17 percent, respectively (Olson et al., 1997). on large farms, had higher water nitrate concentrations dur- The threshold live oocyst count of Giardia and Cryp- ing summer and fall. Agricultural activities, however, differ tosporidium needed to infect horses is unknown. from season to season and consequently skew the nitrate concentration upward or downward during those periods Algae (Ridder et al., 1974). Scottish streams had the highest fluxes of ammonia and nitrate-nitrogen during autumn and winter Cyanophyceae (blue-green) and other algae are being but acute elevations occurred during or following storm increasingly reported as contaminants of water in associa- events (Petry et al., 2002). tion with the eutrophication of worldwide water supplies (de Figueiredo et al., 2004). More importantly, the genera Microcystis, Aphanizomenon, Planktothrix/Oscillataria, Protozoa Nostoc, and Anabaena produce highly toxic hepatotoxins Two common pathogenic protozoa in water are Cryp- called microcystins that can affect humans and livestock tosporidium and Giardia but neither protozoal organism (Romanowska-Duda et al., 2002; de Figueiredo et al., typically causes significant disease in horses. The oocysts of 2004). Cyanophytes can cause taste and odor adulteration both Giardia and Cryptosporidium increase markedly in of water described as moldy, musty, grassy, or with a septic- tributaries draining agricultural lands following extreme tank odor. Microcystin-producing algae in the U.S. Mid- rainfalls and flooding (Kistemann et al., 2002) and in the west favored growth in surface waters contaminated with United Kingdom were highest in fall and winter coinciding high total suspended solids, chlorophyll, phosphorus, and with the calving season (Bodley-Tickell et al., 2002). Giar- nitrogen compounds, although these conditions were not dia and Cryptosporidium oocysts are not uncommon in invariable (Graham et al., 2004). The calculated trigger feces of domestic livestock, especially in calves (Olson et value for microcystin-LR in water for horses is 2.3 µg/L or

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138 NUTRIENT REQUIREMENTS OF HORSES 11,500 cells/mL (ANZECC, 2000). These values were Butudom, P., D. J. Barnes, M. W. Davis, B. D. Nielsen, S. W. Eberhart, and based on maximal water intakes and incorporate several H. C. Schott II. 2004. Rehydration fluid temperature affects voluntary drinking in horses dehydrated by furosemide administration and en- safety factors, including lowest observed adverse effects durance exercise. Vet. J. 167:72–80. level and inter- and intraspecies variation, but were not CCME (Canadian Council of Ministers of the Environment). 2002 (up- based on studies in horses. date). Canadian Environmental Quality Guidelines. Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses. Chap- ter 5. Bacteria Collastos, C. 1999. Fluid therapy: when and where? Proc. Am. Assoc. Equine Pract. 45:271–272. Total coliform bacteria and total fecal coliforms are used Crowell-Davis, S. L., K. A. Houpt, and J. Carnevale. 1985. Feeding and as sentinels of water contamination by fecal pollutants. Total drinking behavior of mares and foals with free access to pasture and coliforms are a generic group of gram-negative bacteria that water. J. Anim. Sci. 60:883–889. are distinguished from thermotolerant coliforms (fecal col- Cymbaluk, N. F. 1989.Water balance of horses fed various diets. Equine Pract. 11:19–24. iforms) by a lower tolerance of high temperatures (45°C). Cymbaluk, N. F. 1990a. Comparison of forage digestion by cattle and Thermotolerant bacteria used to be considered more indica- horses. Can. J. Anim. Sci. 70:601–610. tive of fecal contamination by warm-blooded animals, but Cymbaluk N. F. 1990b. Cold housing effects on growth and nutrient de- some thermotolerant coliforms are now known to arise from mand of young horses. J. Anim. Sci. 68:3152–3162. environmental contaminants. Thermotolerant coliforms are Cymbaluk, N. F., M. E. Smart, F. Bristol, and V. A. Pouteaux. 1993. Im- portance of milk replacer intake and composition in rearing orphan more specifically related to Escherichia coli, but can also in- foals. Can. Vet. J. 34:479–486. clude the enterobacteria Klebsiella, Citrobacter, and others. Danielsen, K., L. M. Lawrence, P. Siciliano, D. Powell, and K. Thompson. Both methods of bacterial assessment indicate potential con- 1995. Effect of diet on weight and plasma variables in endurance exer- tamination of water and can be a gauge of the effectiveness cised horses. Equine Vet. J. Suppl. 18:372–377. of water treatment procedures. Increased colony counts of de Figueiredo, D. R., U. M. Azeiteiro, S. M. Esteves, F. J. Goncalves, and M. J. Pereira. 2004. Microcystin-producing blooms—a serious global bacteria and, specifically, fecal streptococci and Clostridium public health issue. Ecotoxicol. Environ. Safety 59:151–153. perfringens were observed in runoff after extensive rainfall Doreau, M., S. Boulot, W. Martin-Rosset, and J. Robelin. 1986. Relation- and after floods of forested or agricultural communities ship between nutrient intake, growth and body composition of the nurs- (Kistemann et al., 2002). ing foal. Reprod. Nutr. Develop. 26:683–690. The median threshold guideline for thermotolerant col- Doreau, M., S. Boulot, and W. Martin-Rosset 1991. Effect of parity and physiological state on intake, milk production and blood parameters in iforms for livestock has been given at 100 thermotolerant lactating mares differing in body size. Anim. Prod. 53:111–118. coliforms/100 mL (ANZECC, 2000). Canadian livestock Doreau, M., S. Boulot, D. Bauchart, J.-P. Barlet, and W. Martin-Rosset. water guidelines do not give a stated threshold coliform 1992. Voluntary intake, milk production and plasma metabolites in number for livestock because of the variation in pathogenic- nursing mares fed two different diets. J. Nutr. 122:992–999. ity of enterobacteria. The coliform bacteria in water most Dulphy, J. P., W. Martin-Rosset, H. 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