ties as shivering to maintain body temperature. Measures of heat production and heat dissipation have been made in chimpanzees at an ambient temperature of 23.9°C, presumably within the thermoneutral zone of this species (Dale et al., 1967). When heat loss was partitioned, losses were approximately equal via radiation, convection, and evaporation of moisture. Basal levels of heat production (or energy expenditure) for chimpanzees with estimated ages from 42 to 74 months and BW from 11.3 to 27.2 kg averaged 2.222 kcal·BWkg-1 hour-1, equivalent to 53 kcal·BWkg-1·day-1.

BMR can be used as a baseline index of daily EE to which that of activity can be added. This basal EE is usually expressed on a metabolic body-weight basis with the equation noted previously—BMR in kcal·day-1 = 70 × BWkg0.75 (Clarke et al., 1977; Lloyd et al., 1978; King, 1978; Feldman and McMahon, 1983; McNab, 1983; Kurland and Pearson, 1986; Nagy, 1987; McNab, 1988; Mori, 1995; Tilden and Oftedal, 1995; Leonard and Robertson, 1997). The true value of the exponent has been debated, and other relative BMR scaling relationships have been described for captive and wild mammals, including primates (Stahl, 1967; Stahl and Malinow, 1967; King, 1978; Heusner, 1985; McNab, 1986; Robbins, 1993a; Stevens and Hume, 1995; Leonard and Robertson, 1997), with consideration of animal type, species, and quality of diet (Ross, 1992).

In housed domestic or wild animals, energy in addition to basal requirements for ingestion and metabolism of food is required, but little is needed for thermoregulation or physical activity (Curtis, 1983; Stevens and Hume, 1995). Under these husbandry conditions, ME requirements for daily maintenance are about double the BMR of 293kJ (70 kcal) × BWkg0.75 for eutherians (Kleiber, 1961; Robbins, 1993a). Voluntary ME intakes of 120 species of zoo animals, grouped in families (including primates), were related to their predicted BMR requirements (Evans and Miller, 1968). The mean ME intake, 146 kcal × BWkg0.75 was about twice the energy required for basal metabolism, or 2.08 × BMR.

The reported addition to BMR to accommodate minimal physical activity (minimal survival requirement) of humans was 1.27 × BMR (89 kcal × BWkg0.75), increasing to 1.4 × BMR (98 kcal × BWkg0.75) over 24 hours if 1.5 hours· day-1 of walking or 2 hours·day-1 of standing was included. The 1.4 value serves as a guide for estimating maintenance ME requirements of humans (FAO/WHO/UNU, 1985). A factor of 1.3 × BMR (91 kcal × BWkg0.75) has been proposed as a maintenance ME requirement for carnivores and omnivores (Scott, 1986), whereas a maintenance ME requirement of 1.5 × BMR (105 kcal × BWkg0.75) has been proposed for a range of animals when relative energy requirements were determined by a factorial approach similar to that used for estimating protein requirements (Payne and Waterlow, 1971). With increasing activity of adult omnivores (including humans) and adjustment of BMR for HI, 2 × BMR (140 kcal × BWkg0.75) has been proposed as the maintenance ME requirement for moderate activity and 3 × BMR (210 kcal × BWkg0.75) for high activity (Scott, 1986). Net costs for standing require a 20% energy increase above basal for mammals, or 1.2 × BMR (84 × BWkg0.75) (Robbins, 1993a). The energy requirement for terrestrial locomotion (TL) is an inverse function of BW, and bipeds and quadrupeds can be represented with the same regression equation, Ykcal·BWkg-1·TL·km-1 = 2.57 × BWkg-0.316 (Taylor et al., 1982). Climbing adds an average of 6 kcal·BWkg-1·per vertical kilometer climbed (Robbins, 1993a). The cost of brachiation (use of the arms to swing between objects) varies with speed, and the net cost (kcal·BWkg-1·km-1) is 1.5 times as high as for normal walking by spider monkeys (Parsons and Taylor, 1977). Hanging motionless was reported to increase resting metabolism of the spider monkey and slow loris by 65 ± 32%, which is 3 times more costly than the 20% increment for standing over resting in mammals. When energy expenditures over 24-hour periods were measured in 177 closely observed human subjects, it was demonstrated that much of the variability in daily energy expenditure, independent of differences in body size, was due to differences in spontaneous physical activity, or fidgeting. This activity accounted for energy expenditures of 100-800 kcal·d-1 in these subjects (Ravussin et al., 1986) and might apply to nonhuman primates as well.

Clinical practitioners often use a simplified formula (1 kcal·BWkg-1·hour-1) to approximate average daily basal energy requirements of adult humans (Williams, 1997). Adjustments for various levels of activity may be added to this basal estimate as follows: 20%, 30%, 40%, or 50% for very sedentary, sedentary, moderately active, or very active, respectively. The normal activity of most free-living animals would be considered sedentary to moderate, requiring an energy expenditure addition of 30%-40% to the BMR. Caged animals generally would require additions of only 13%-35% to the maintenance requirement for activity (Lloyd et al., 1978; Scott, 1986).

Daily total EE, the sum of all caloric costs for maintenance and activity of male and female adult wild howlers, Alouatta palliata, estimated with the DLW method, averaged 85 kcal·BWkg-1 or 135 kcal·BWkg0.75 (Nagy and Milton, 1979). By comparison, the mean total EE of adult caged M. mulatta, also determined with DLW, was 87 kcal·BWkg-1·day-1 (Stein et al., 1996). The total 24-hour EE of ad libitum-fed adult M. mulatta ranged between 112 and 73 kcal·BWkg-1 when measured with DLW (Lane et al., 1995).

The 24-hour EE of prepubertal male and female chimpanzees, determined with indirect calorimetry, were about 65 and 56 kcal·BWkg-1, respectively (Dale et al., 1967). The mean daily EE of two adult male and two adult female Gelada baboons, measured with indirect calorimetry, was

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