maintained their water balance by selecting a diet comprising largely succulent new leaves (Glander, 1978).
Quantitative data on liquid-water consumption are available for few species of nonhuman primates. Pace et al. (1964) reported that three adult pig-tailed macaques (Macaca nemestrina) fed a dry commercial diet consumed gross energy (GE) at 70 kcal·kg-1 of body weight and water at 1 ml·kcal-1 of GE. Kerr (1972) concluded that consumption of water at 1 ml·kcal-1 of GE was a reasonable estimate of liquid-water intake. Schroederus et al. (1999) measured baseline water intakes in adult rhesus monkeys of both sexes. Older monkeys (20-36 years) drank 380 ± 63 ml·d-1, significantly less (P < 0.05) than the 679 ± 92 ml·d-1 consumed by middle-aged (13-17 years) monkeys or the 750 ± 128 ml·d-1 consumed by young adults (7-9 years).
Patterns of eating and drinking were studied in five adult male rhesus macaques housed in individual cages and provided food and water ad libitum. Animal weights and ambient temperatures and relative humidity were not given, but the light:dark cycle was 12:12. Purina Monkey Chow 5040® providing metabolizable energy (ME) at an estimated 4 kcal·g-1 (air-dry) was fed. Mean daily food consumption was 126.8 g and mean daily liquid-water consumption was 440 ml. Thus, daily liquid-water consumption was 3.5 ml·g-1 of air-dry diet or 0.87 ml·kcal-1 of ME consumed (Natelson and Bonbright, Jr., 1978).
Six rhesus macaques were housed in individual cages at an ambient temperature of 24-29°C, a relative humidity of 75-80%, and a light:dark cycle of 12:12 (Zorbas et al., 1997). They were 3-4 years old and had a mean body weight of 5.58 kg. They had ad libitum access to a commercial dry diet and liquid water. Food intake was not reported, but mean water intake was 679 ml·d-1 or 122 ml·BWkg-1·d-1.
Daily food and water intakes of 253 wild-origin cynomolgus macaques (Macaca fascicularis) kept in individual cages were determined (Suzuki et al., 1989). Mean (± SD) body weight of 61 males was 6.5 ± 1.3 kg and of 192 females 3.4 ± 0.9 kg. They were fed a dry commercial primate diet plus apples and oranges. Mean (± SD) drinking-water intake by males was 50 ± 33 ml·BWkg-1·d-1 and by females 49 ± 48 ml·BWkg-1·d-1. Mean (± SD) total water intake from drinking water and food by males was 76 ± 35 ml· BWkg-1·d-1 and by females 100 ± 51 ml·BWkg-1·d-1.
Preformed-water concentration in ingested food varies greatly with the diet but accounts for about one-third of water intake by humans (Askew, 1996). Most foods contain some water, and water in the edible portions of cultivated fruits and vegetables generally makes up 80-95% of their mass (National Research Council, 1989; Holland et al., 1991). Preformed water in the foods of free-ranging nonhuman primates can be as little as about 2-3% of air-dried seeds in hot deserts or over 70% of the fresh weight of succulent plant parts in a tropical rainforest (Baranga, 1982; Calvert, 1985; Rogers et al., 1990; Barton et al., 1993; Robbins, 1993; Edwards, 1995).
The gross yield of metabolic water from oxidation of 100 g of carbohydrate, protein, and fat is about 60, 41, and 107 g, respectively (Askew, 1996). However, excretion of the urea produced during protein oxidation requires nearly all the metabolic water released. Thus, there is no net water yield from oxidation of protein. Metabolic water furnishes about 8-10% of the water needs of humans (Askew, 1996). If 100 g of a nonhuman-primate diet contained 16% digestible protein, 10% digestible fat, and 50% digestible carbohydrate, complete oxidation of these three fractions would have a net yield of about 40 ml of metabolic water, or about 1 ml per 8.8 kcal of ME.
Metabolic water is also generated during muscular activity through catabolism of stored glycogen and fat. However, the anaerobic metabolism of glucose to lactate (associated with intense effort) yields only one-third as much water as does complete glucose oxidation, and the metabolic-water contribution from either anaerobic or aerobic effort is still a small proportion of total body water (Askew, 1996).
Water is lost from the body mainly via the lungs, skin, intestine, and kidneys, although losses also occur via menstruation and lactation (Widdowson, 1987; Harris and Van Horn, 1992; Askew, 1996).
In the absence of sweating, about 44% of total water loss from the human body is insensible water vapor from the lungs or from diffusion through the skin (National Research Council, 1989). These insensible losses increase under conditions of high ambient temperature, high altitude, and low relative humidity. Perspiration increases human water loss further, but there is little information on the presence of sweat glands and sweating in nonhuman primates.
Water concentration of feces varies with diet but in healthy adult humans is about 70% (Askew, 1996). In the absence of sweating, water in the normal human stool makes up about 3-4% of total daily water loss; diarrhea can greatly increase this figure (National Research Council, 1989). Cotton-top tamarins (Saguinus oedipus) frequently exhibit colitis in a laboratory environment, and daily fecal output of tamarins with mild, moderate, or severe colitis was 6.0, 7.6, or 8.1 g·BWkg-1, respectively. Water concentrations were 49.4% or 55.0% in the feces of tamarins with mild or moderate colitis (Stonebrook et al., 1996). Suzuki