The transition from milk/formula to solid foods is a gradual process that relies heavily on observational learning. In the wild, young gibbons would eat milk for a year or longer, but start to try solid foods much earlier. When hand reared, it is generally recommended to wean them much earlier, as this will save valuable resources, and enable the socialisation of the youngster with other gibbons, which is very important for later life.
Before physical foods are ever offered, caregivers should allow the infant to watch them and/or other gibbons eat, and letting the infant smell the food. This inspires natural curiosity and is an essential part of the gibbon’s learning process. Solid foods are generally introduced when the infant begins to show active interest and their teeth begin to erupt. In hand reared gibbons this is generally from 2.5-3 months of age. The initial foods offered should mirror the adult diet but can be modified by cooking for easier chewing. It is recommended to introduce vegetables before adding any fruits to the diet. Cooking should be phased out as soon as the infant is reliably eating each food item.
To prevent diarrhea it is important to take a gradual approach, adding one new item at a time. Caregivers should hold the infant in an upright position, smash very small bites between their fingers, and place it in the infant’s mouth, ensuring they swallow all food entirely before offering more. As the infant accepts the food, portion sizes can be increased. As solid foods are successfully integrated, night bottles can be discontinued, and daytime milk feedings can be stretched to once every four hours. During this phase, food should be placed close to the infant while they are near conspecifics so they can observe adult gibbons eating, providing helpful preparation for their eventual introduction to a group. The weaning process can be completed by 6-7 months of age, though individual variation can influence this.
The weaning process is rarely without challenges, and caregivers must be prepared to manage several common complications. One frequent issue is that during weaning the weight gain stops and the weight reaches a plateau. As the infant transitions from highly digestible formula to solid foods, they may expend more energy learning to process the new diet or simply not consume enough volume initially, causing their weight gain to temporarily stall. Therefore, body weight should be recorded daily in this period. Caregivers should closely monitor the infant to ensure they are actively swallowing the solids, and avoid the temptation to drastically increase formula back to original levels, which can further deter the infant from eating solids.
Diarrhoea is another common complication during the weaning phase. Overfilling the stomach beyond its natural capacity, which is estimated at 50 ml/kg for most species, can lead to gastrointestinal upset, decreased transit time, and severe diarrhea. Caregivers must monitor the condition of the feces closely. Taking the gradual approach of introducing one item at a time ensures that if diarrhea develops, staff can easily identify and eliminate the offending food. If diarrhea occurs, caregivers should temporarily substitute some formula volume with sterile oral rehydration salts (ORS) to prevent dehydration and consult veterinary staff immediately. Another possible reason for diarrhoea is that young gibbons don’t have the necessary microbes in their guts to digest the new food items. In the wild they’d acquire this from their parents. In human care, it is known that primates frequently have a human-like gut microbiome, likely due to the close human-primate relationship. Pre- and probiotics may be helpful in this situation, and with diarrhoea in general.
Finally, caregivers frequently encounter resistance from the youngster when attempting to introduce new foods or completely phase out milk. Primate infants often experience a period of “weaning conflict,” where the infant may throw tantrums, reject solids, or aggressively demand milk as they are progressing toward independence. Hand-reared gibbons display similar resistance and may regress in their feeding habits. To overcome this, caregivers must remain patient and highly consistent. Offering familiar, formula-soaked foods can help bridge the sensory gap, and ensuring the infant observes conspecifics eating nearby will naturally stimulate their innate drive to forage for solid foods alongside their peers. Importantly, by the end of the weaning period, all milk formula should be phased out.