The great ape section at Twycross Zoo consisted of 42 apes. All of these animals had historically been given a partly fruit based diet, combined with vegetables, two types of pellet and a protein element. Some of the apes were perfectly healthy, whilst others experienced dental issues and also carried excess weight which had led to other medical issues.

After a diet review, it was decided to change the diet substantially. Firstly, the eggs were removed from the diet  completely and replaced with nuts and seeds. This lowered the overall amount of protein in the diet and provided a larger amount of smaller items that could be used as a scatter feed as most of the ape groups were of a considerable size. This change was made immediately, with no negative effects.

Next the pellet was condensed into just one type. The primate pellet that was being used showed higher levels of proteins and sugars with far less fibre than the leafeater pellet so the energy content of the diet was kept the same, but only using the leafeater pellet and removing the other one completely. This again did not need a transition period as the apes were already accustomed to eating the leafeater pellet in a smaller quantity.

The next step was to decrease and eventually completely remove the fruit from the diet. Fruit cultivated for human consumption has a much higher sugar content than the natural fruits found in the habitats of the great apes and so is unnecessary in a zoo diet. Again, we retained energy content of the original diet, but changed its nutritional composition by swapping some of the fruit for certain vegetables, adding more fibre and decreasing the amount of simple sugars. The fruit was decreased first by 25% and then another 25%. Once the fruit was at 50% of its usual amount then it was removed completely and substituted for a range of vegetables in the same way as before. The reason the fruit was only decreased to 50% and then taken out completely was to avoid food based aggression in the larger groups where dominant animals could monopolise smaller amounts of high value items such as fruit.

Once the diets had been changed it was still found to be fairly low in fibre in comparison to a natural diet and the great ape husbandry guidelines. Therefore we looked into browse in more depth. Browse provision is very  important in all great ape species. Not only does it provide much needed fibre and roughage to the diet, but has behavioural benefits such as encouraging food manipulation through stripping of the bark which increases the apes' activity and foraging time extensively. It also holds practical implications such as nest building opportunities and encourages natural behaviours such as termite fishing, when the apes will use the sticks to fish for items in faux termite mounds and puzzle feeders.

Once the diet change was complete it was important for the team to observe behaviour and monitor weight as well  as other medical issues to ensure the diet change was as effective as it could be.