Great ape nutrition: low-sugar and high-fibre diets can lead to increased natural behaviours, decreased regurgitation and reingestion, and reversal of prediabetes

Abstract

Great apes in captivity have been affected by a variety of conditions, including obesity, heart, gastrointestinal and dental diseases, and diabetes, all of which are at least influenced by an inappropriate diet. ‘Regurgitation and reingestion’ is also related to diet in great apes. Diets tend to be high in water-soluble carbohydrates (WSC) (e.g. sugars and starches) and low in fibre. This study aimed to reduce the WSC and increase fibre concentrations of great ape diets, most notably for Chimpanzees Pan troglodytes, Bornean orangutans Pongo pygmaeus, Sumatran orangutans Pongo abelii and hybrid orangutans, and Western lowland gorillas Gorilla gorilla gorilla, and evaluate the behavioural and physiological responses of these species to the dietary changes. Wildlife Reserves Singapore had 4.8 Chimpanzees, 10.5 Bornean orangutans, 5.3 Sumatran orangutans and 2.1 P. pygmaeus × P. abelii orangutan hybrids, and Longleat Safari and Adventure Park, UK, had 4.0 Western lowland gorillas. Behaviour was recorded via scan sampling throughout the diet-change process with a gradual decline in WSC. Five orangutans and two Chimpanzees were conditioned for finger pricking to monitor their blood-glucose concentrations. The new diets led to changes in WSC from 59·0–64·3% to 47·5–47·7% and in neutral detergent fibre from 11·5–14·4% to 15·7–22·9% on a dry-matter basis. These dietary changes significantly increased ‘travelling’, ‘foraging’ and ‘social affiliative’ behaviours, and decreased ‘inactivity’ and ‘abnormal behaviour patterns’, such as ‘regurgitation and reingestion’. Fasting blood glucose also decreased and, eventually, all great apes sampled had average blood-glucose levels. Orangutans had a stronger insulin response compared with Chimpanzees, which may reflect their feeding ecology.