94 kcal·BWkg0.75 or 1.34 × BMR (Iwamoto, 1979). When EE was estimated from ME intake and BMR was calculated (70 kcal·BWkg0.75) as presented in Table 2-1, the daily ME requirement for lean adult squirrel monkeys was 184 kcal·BWkg0.75 (2.63 × BMR) compared with 152 kcal·BWkg0.75 (2.17 × BMR) for obese squirrel monkeys (Ausman et al., 1985).

A study comparing energy intakes and requirements among adults of three primate families found ME intakes of 137-255 kcal·BWkg0.75 by marmosets (Callitrichidae), 87.9-118 kcal·BWkg0.75 by apes (Pongidae), and 86.3-122.8 kcal·BWkg0.75 by lemurs (Lemuridae)(King, 1978). Those ME intakes were equivalent to an average of 198, 34, and 78 kcal·BWkg-1·day-1 for the three groups, respectively (Table 2-2). For marmosets, the average ME intake was 2.07 × BMR, whereas for both lemurs and apes, ME intake was about 1.4 × BMR (for BMRs shown in Table 2-1).

Body weights were sustained in adult male and female rhesus monkeys (M. mulatta) when animals were fed an amount of a commercial diet (3.47 kcal ME·g-1) targeted to meet an expected daily maintenance requirement of 93 kcal·BWkg0.75 (Robbins and Gavan, 1966). Daily estimated ME intakes of 40.8 kcal·BWkg-1 for males and 42.2 kcal·BWkg-1 for females were less than those reported for M. mulatta in other studies (Table 2-2).

Adult female baboons (Papio sp.), weighing an average of 15.6 kg, were fed a commercial diet (about 3.1 kcal ME·g-1) providing an average ME intake of 48 kcal·BWkg-1·d-1 (Table 2-2). That energy intake apparently met maintenance requirements on the basis of sustained body weights over a 4-week period (Wene et al., 1982).

Mixed zoo diets containing an average calculated ME concentration of 3.6 kcal·g-1 and fed ad libitum to adult female proboscis monkeys (Nasalis larvatus) with an estimated mean body weight of 9 kg resulted in an estimated maintenance ME requirement of 3 × BMR, 1.5 times as great as the predicted maintenance requirement (2 × BMR) based upon body weight (Dierenfeld et al., 1992) (Table 2-1).

Intakes of mixed diets by adult wild and captive aye-ayes (Daubentonia madagascariensis) were measured, and ME intakes were estimated to be 260-342 and 260 kcal· day-1 for wild and captive animals, respectively. A combined daily ME requirement was established at 280 kcal (Sterling et al., 1994). The ME intake by captive aye-ayes in relation to body weight was 106 kcal·BWkg-1·day-1 (Table 2-2).

Wild adult female and male orangutans (Pongo pygmaeus) have been estimated to weigh an average of 37.8 and 83.6 kg, respectively (Rodman, 1984). For an estimated ME requirement of 40 kcal·kg-1·day-1, the daily ME requirements of the female and male orangutans would be 1,512 and 3,344 kcal, respectively. During the month of greatest fruit consumption, wild adult female and male orangutans of unknown weight consumed an estimated 7,404 and 8,422 kcal ME·day-1, respectively. During the month of lowest fruit consumption, female and male orangutans consumed only an estimated 1,793 and 3,824 kcal ME·day-1, respectively (Knott, 1998). Although energy intakes during the period of low fruit availability appear adequate, on the basis of the above estimates of body weight and ME requirements, urinary ketone concentrations indicated that the wild orangutans were not maintaining energy balance but were losing weight.

Commercial diets for long-term maintenance of marmosets and tamarins, formulated to contain 3.5-4.2 kcal ME·g-1, have helped to prevent “marmoset wasting syndrome” among Callithrix jaccus, C. jaccus jaccus, C. jaccus penicillata, Saguinus oedipus oedipus, and S. fuscicollis illigeri (Wirth and Buselmaier, 1982; Clapp and Tardif, 1985). Purified diets fed to adult male cotton-top tamarins (Saguinus oedipus) and providing 160 kcal GE·BWkg-1· day-1 (154 kcal ME·BWkg-1·day-1) (Table 2-2) alleviated signs of the wasting syndrome (Escajadillo et al., 1981). An open-formula, natural-ingredient diet providing 335 kcal GE·BWkg-1·day-1 (232 kcal ME·BWkg-1·day-1) (Table 2-2) alleviated signs of the wasting syndrome in mustached tamarins (Saguinus mystax) (Barnard et al., 1988). The daily ME intake for maintenance of adult cotton-top tamarins (Saguinus oedipus oedipus) was found to decrease with age—208 kcal·BWkg-1 for a 2-year-old male and 113 kcal·BWkg-1 for an aged male (Kirkwood and Underwood, 1984).

Energy Requirements for Growth

Infant nonhuman primates require more energy per unit of BW for growth than do adults of their species (Stahl and Malinow, 1967; Kerr, 1972; Nicolosi and Hunt, 1979; King, 1978; Ausman, 1995). Energy requirements for growth depend on the rate and composition of gain, which can vary, particularly among wild animals influenced by seasonally variable environments (Robbins, 1993b). The mass-specific BMRs of young, rapidly growing animals are higher than those of adults because body surface area per unit of body mass is greater in the young (Scott, 1986; Robbins, 1993b); the mass-specific BMR can reach 3-4 times that of the adult (Clarke et al., 1977).

Although growth of an animal is commonly described by a sigmoid curve, most of the growth occurs during a relatively linear intermediate phase. Maximal growth rates of the young of different species during this linear phase tend to increase as a power function of adult BW. The relationship between adult BW (X in g) and growth rate (Y in g·day-1) of neonates in 160 species of placental mammals has been calculated to be Y = 0.0326X0.75 (r2 = 0.94). The same relationship in 32 species of primates was calculated to be Y = 0.2165X0.35 (r2 = 0.66) (Robbins,

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