et al. (1989) reported that mean daily fecal outputs of captive cynomolgus macaques were 3.0 and 3.9 g·BWkg-1 for males and females, respectively, but they did not report fecal moisture concentrations. Mean daily total water intakes (drinking water plus water in food) by males and females were 76 and 100 g·BWkg-1, respectively. If these primates were in water balance, water intakes plus metabolic water would be equaled by water loss. Assuming fecal water concentrations of 50-70%, fecal water loss would be equivalent to 2-3% of total water intake. If it were possible to account for the contribution of metabolic water to water balance, fecal water loss presumably would be a still lower percentage of total water loss.

The majority of total water loss in nonsweating humans, about 53%, is lost as urine (National Research Council, 1989). Because the concentrating ability of the adult human kidney is limited to about 1,400 mOsm·L-1, the amount of waste that must be excreted by the kidneys dictates the minimal volume of water required for urine formation. Much of the waste comes from products of protein catabolism, such as urea, sulfates, phosphates, and other electrolytes. Several studies have found that rhesus macaques fed a dry commercial diet excreted urine at about 20-50 ml·BWkg-1·d-1 (National Research Council, 1978). Male and female cynomolgus macaques fed a dry commercial diet plus apples and oranges excreted urine at 21 and 27 ml· BWkg-1·d-1, respectively, or about 27% of the total water intake from drinking water and food (Suzuki et al., 1989). Common marmosets (Callithrix jacchus) were placed in metabolism cages for 24 hours without food but with ad libitum access to water. Mean water intakes during 161 observations were 11.7 ml, whereas mean urine volumes were 12.6 ml (Lunn, 1989).

In controlled laboratory studies with adult male lesser mouse lemurs (Microcebus murinus), it has been demonstrated that photoperiod and diurnal variations in activity can influence water loss (Perret et al., 1998). This lemur is a small, arboreal, nocturnal prosimian found near the south coast of Madagascar. Its winter environment is dry and up to 20°C cooler (considering both diurnal and seasonal differences), and more limited in resources than the rainy summer environment. Daylength at the winter solstice is 10 hours 50 minutes and at the summer solstice is 13 hours 20 minutes. As days shorten and preparation for winter begins, the animals fatten and decrease their locomotor activity, whereas reproduction occurs during the lengthening days of late spring and early summer. Lesser mouse lemurs were subjected in the laboratory to a constant temperature (24-26°C), 55% relative humidity, and short days (light:dark ratio, 8:16) for 14 weeks, followed by long days (L:D, 14:10) for 22 weeks. Initial mean (± SEM) body mass was 97 ± 3 g; it increased to a maximum of 125 ± 4 g after exposure to short days. After exposure to long days, mean body mass declined to 77 ± 3 g. Total water loss declined during short-day exposure to 38 ± 0.3 mg·BWg-1·day-1 after 3 months and increased during long-day exposure to 87 ± 7 mg·BWg-1·day-1 after 2 months. When measured in a post absorptive state (no food or water during 24 hours), water in feces accounted for less than 0.5% of total water loss and water in urine about 37%, and the remainder was presumably evaporative water loss. Urine was voided only at the beginning of the nocturnal active period, and total water loss at night was always greater than during the daily sleeping period.

Dehydration is a common cause of fluid and electrolyte imbalance in elderly humans and, if not properly managed, can lead to central nervous system dysfunction, convulsions, coma, and death (Miller, 1987). It has been suggested that this susceptibility to dehydration resides in impaired regulation of thirst, impaired urine-concentrating ability, or both. The issue has been studied in monkeys by Schroederus et al. (1999). Although elderly rhesus macaques (20-36 years old) drank less during a baseline period than did younger macaques (7-17 years old), the elderly macaques responded to 24-hour water deprivation by eating less and concentrating their urine to the same degree as the younger macaques. During a postdeprivation compensation period, water intakes of elderly and younger macaques returned to predeprivation levels.

According to Harris and Van Horn (1992), animals can lose nearly all the fat and about half the protein of the body and still survive, but a loss of about one-tenth of total body water results in death. Even moderate restriction of water sources will generally diminish food consumption (National Research Council, 1981, 1986).

WATER QUALITY

Analyses of surface water and groundwater by geologic, agricultural, and public-health agencies have established the presence of variable concentrations of essential and nonessential mineral elements (National Research Council, 1974). In some cases, concentrations of essential minerals can be high enough to contribute substantially to meeting total nutrient needs (National Research Council, 1974, 1980). In others, mineral concentrations can be infinitesimal or excessive and potentially toxic. Because streams, lakes, and private wells are widely used by agricultural interests, these issues are of particular importance to farm families and their livestock. Water-quality guidelines for livestock and poultry were developed (National Research Council, 1974); they are commonly updated in publications in the National Research Council Nutrient Requirements series as they are revised.

In contrast with agricultural animals, captive nonhuman primates usually get their water from municipal water systems just as do most humans in the United States. Although



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