Factors influencing nutrient intake and balance in a group of captive chimpanzees at Twycross Zoo

Consuming the correct food items to reach nutrient requirements is fundamental to an animal’s behaviour, health and reproductive success. Understanding feeding ecology and nutritional goals is necessary for effective captive dietary management. In captivity, the optimal nutrition can aid successful reproduction, overall health and contribute to positive welfare, whilst inadequate nutrition can contribute to the presence of stereotypic behaviours or health conditions such as obesity or diabetes. In wild chimpanzees, dominant individuals can show a less diverse diet than more subordinate individuals, and males generally spend less time feeding than females. However, there is limited research on whether captive animals show different feeding strategies (e.g. consuming varying amounts of different types of food, or spending different amounts of time feeding), or whether individuals consume different amounts of nutrients overall. The aim of this thesis is to determine whether dominance rank or sex influences energy or nutrient intake of macro- and micro-nutrients in captive chimpanzees. I will calculate the energy and nutrient intake of individual chimpanzees and use the Geometric Framework of Nutrition (GFN) to examine the proportional intake of macronutrients consumed and examine the ratio of energy consumed from non-protein (NPE) (carbohydrates, fats and fibre) to protein (P) sources. The food intake of 11 adult chimpanzees housed at Twycross Zoo, UK, was recorded between July and October 2021 (N=55 days). Each day, I observed one individual continuously during every feed to record the number of food items consumed, food unit size (the size of food consumed, e.g. whole or slice), and the time spent feeding. I calculated the quantities of different food categories consumed (pellet, nuts, root vegetables, other vegetables and leafy vegetables) and the total amount of nutrients consumed per day, using the daily food intakes and published nutritional compositions for each food item. Six chimpanzee keepers ranked the dominance hierarchy of chimpanzees, which were later categorized into high, mid and low ranking. Linear Mixed Models were used to determine whether sex and/or dominance rank influenced the daily intake of dry matter, energy, macronutrients or micronutrients. The GFN was used to assess and visualise the chimpanzees’ proportional intake of macronutrients to energy intake.

Results showed that females consumed more energy, dry matter, total non-structural carbohydrates and ash than male chimpanzees, when data were controlled for body weight. Males generally consumed more nuts than females, whilst females consumed more of all categories of vegetables than males, although this was not statistically significant. Dominance ranking was not found to influence food, nutrient, or energy intake. The GFN revealed that the Twycross chimpanzees regulated protein intake, allowing carbohydrates and fats to fluctuate, which has also been seen in wild chimpanzees. NPE:P intake was 3.6:1; half that seen in wild chimpanzees at 7:1 and 10:1 respectively. Males and females appeared to use different feeding strategies to reach the same nutritional goal of protein regulation. Overall, chimpanzees consumed a nutrient intake similar to recommended guidelines, though some chimpanzees showed higher body condition scores than the ideal score, suggesting energy intake may be higher than necessary for some individuals.

Feeding a cultivated fruit-free diet provides more protein and less total non-structural carbohydrates than fruit diets and may allow chimpanzees to reach their protein intake target without overconsuming carbohydrates or calories compared with feeding a fruit diet. My research shows that captive chimpanzees have similar nutritional goals to wild chimpanzees and adds to the growing body of literature promoting the benefits of fruit-free diets; previous research has shown fruit-free diets reduce aggression, dental problems, and body weight in overweight animals. Future research should investigate individual nutrient and energy intake in groups of chimpanzees fed on a fruit diet using the GFN and investigate whether dominance ranking affects nutrient intake in other groups of chimpanzees. Additionally, future work could consider the impact of energy expenditure for male and female chimpanzees, to determine whether females require increased energy intake.