Schmidt, D 2004. Orangutan Husbandry Manual.
Free-ranging orangutans (Pongo pygmaeus in Borneo and P. abelii in Sumatra) have reported average body weights of 86.3 kg (range 80 – 91 kg) for males and 38.7 kg (range 33 – 45 kg) for females (Markham and Groves, 1990). Knott (1999) estimated energy expenditure for adults during peak fruiting season as approximately 3,400 kcal·day-1 for males and 1,900 kcal·day-1 for females (without maternal costs). During periods of low fruit availability energy expenditure fell to an estimated 3,100 kcal·day-1 for males and 1,800 kcal·day-1 for females without maternal costs. Estimated energy demands of 2,300 – 2,400 kcal·day-1 remained the same during high and low fruiting periods for females who were pregnant, lactating, and/or carrying an offspring. These requirements are probably lower for captive animals depending on an individual’s activity level.
Orangutans are classified as “frugivores” because they typically feed on fruits when available. When fruits are not readily available, orangutans consume leaves, bark, pith, flowers, insects, and honey (Galdikas, 1988; Hamilton and Galdikas, 1994; Knott, 1998a, 1999; Leighton, 1993; MacKinnon, 1974; Rodman, 1977). On average, orangutans can be expected to consume each day 1 – 2 % of their body weight in food (on a dry matter basis).
Recommendations are to offer orangutans 14% of their diet (as fed basis) as nutritionally complete primate biscuits and the remaining 86% as produce (as fed basis), with significantly higher proportions of raw vegetables and leafy green vegetables than fruit. These proportions translate in to 50% biscuits and 50% produce on a dry matter basis. Adjustments should be made based on animal body condition, health, activity level, reproductive status, growth stage, and intake. Do not offer too much food, allowing the orangutan to be satiated on produce alone. See appendices for diet examples.