Gibbons naturally maintain a prolonged period of maternal dependency, nursing for up to two years and remaining with the family unit until sexual maturity around 6 to 8 years of age. Hand-rearing neonates is labour and resource intensive and should only be attempted when other options, for example fostering, are not available.
Caregivers must first check the infant for signs of dehydration, ensuring the mouth is moist and the gums are pink. The infant’s body temperature must be normal before offering food. Hypothermia (a body temperature below 36°C) is an important risk for very young gibbons, and must be corrected as a matter of priority. If hypothermic, neonates should be placed in an incubator. If a commercial incubator is unavailable, a secure, draft-free enclosure utilising heat pads or heat lamps can be used, aiming to maintain a constant ambient temperature of approximately 30°C. Newborn gibbons cannot appropriately regulate their body temperature in the first few weeks of life, therefore, it is important to keep them warm, and prevent both hypothermia, as well as overheating.
Human milk formulas can be successfully used for gibbons, and provide a convenient option where available. Standard commercial human infant formulas sourced from local pharmacies work well. Low-iron or soy-based varieties are ideal, or standard formulas can be mixed with generic pediatric lactase drops to aid digestion if lactose intolerance occurs. In most cases formula is given from a bottle with an appropriately sized nipple, but in some cases, especially for very young animals feeding from a syringe might also be suitable early on. The size of the opening on the nipple is important. Too small opening means the infant needs to work too hard for the milk and will get frustrated and hungry. However, too large holes can lead to milk pouring into the mouth, and consequently, to aspirational pneumonia. Bottles should generally not leak significant amount of milk when tipped upside down, unless there is suction applied on the nipple. It is recommended to source “slow-flow” or premature infant nipples, as restricting the flow rate is a key preventative measure against aspiration. Overused, leaking nipples should be replaced. The formula needs to be dissolved in body warm, but not overly hot, water. The temperature should be carefully tested on the wrist before being offered to the infant.
Formula calculations are important to prevent complications, especially in the early stages of the hand rearing process. Initial daily formula volumes should be about 10% of the infant’s body weight. It is common practice to gradually introduce formula over 24-36 hours, starting with formula mixed with equal amount of sterile electrolyte or oral rehydration salts. The amount of electrolyte is then gradually decreased at every feed, reaching full strength formula by the end of the first 24-36h. This gradual process may prevent diarrhoea, however, it is likely that the food won’t meet the infant’s energy requirements, which will lead to some weight loss. If the infant tolerates the full strength formula but fails to gain weight, the volume can be slowly increased to 15-20% of their body weight per day. To calculate the amount to be fed at each feeding, the daily volume should be divided by the number of feeds.
For approximately the first three months, infants must be bottle-fed every two to three hours, with milk offered in an upright position to prevent aspiration. If the infant becomes excessively hungry between scheduled feedings, caregivers may offer small amounts of pedialyte or water, equivalent to about half the volume of their regular formula. Immediately following each feed, staff must gently stimulate the infant’s perineal area using a damp cotton ball or gauze pad to encourage essential urination and defecation, recording all output on nursery logs. A useful health monitoring step is to routinely measure the infant’s waist circumference (measuring at the level of the bottom of the navel) with a soft measuring tape to monitor for gastric distention, which is an early warning sign of enteritis. After feeding, bottles must be thoroughly disinfected with soapy water, boiled, and laid out to dry.
When raising youngsters it may be important to expose them daily to unfiltered sunlight. Hand reared gibbons have grown up with long bone deformation when relying solely on formula in the absence of natural UVB radiation (sunlight) which stimulates vitamin D synthesis. Alternatively, if it is not possible to provide enough sunlight, vitamin D should be added to the diet, in the form of drops, which are available for human babies from pharmacies.