Early hand-rearing of a premature Western lowland gorilla (Gorilla gorilla gorilla) at the Fort Worth Zoo
Citation
Ward AM. 2025. Early hand-rearing of a premature Western lowland gorilla (Gorilla gorilla gorilla) at the Fort Worth Zoo. In Treiber K, Brooks M, D’amato-Anderson J, Nylander J, Eds. Proceedings of the Sixteenth Conference on Zoo and Wildlife Nutrition, AZA Nutrition Advisory Group, Oklahoma City, OK.
Abstract
In January 2024, a 33-year-old Western lowland gorilla (Gorilla gorilla gorilla), gave birth to a 4-to-6-week premature female infant via cesarean section. Despite repeated attempts to reunite the mother and baby, the mother showed little interest in caring for her baby. Based on a gorilla gestation of 35 weeks, at day 0 her gestational age was considered 31 weeks. Fort Worth staff hand-reared the infant to 82 days post birth, a gestational age of 42.2 weeks at which time she was transferred to the Cleveland Zoo/a surrogate mother and successfully integrated into their troop.
Though differences exist between gorilla milk and human infant formulas, in general gorilla milk is higher in protein (significantly higher on an energy basis) and lower in fat (until late lactation) (Table 1), human formulas have been used successfully to hand-rear gorillas and are recommended in the Association of Zoo and Aquarium’s Animal Care Manual for Western lowland gorilla (Gorilla gorilla gorilla) (2017). Fort Worth Zoo staff worked closely with a local neonatologist on the oral feeding plan and methods of assessment. Additionally, data from a premature gorilla raised at the Cleveland Zoo contributed significantly to plans and assessment.
Similar to human premature infants, this infant was fed the higher energy human formula Enfamil NeuroPro EnfaCare Premature Infant 22 kcal/oz. Formula was fed full strength at 8% of body weight (BW) on day 1, with a plan to gradually increase to 16% by day 6. Initial feeds were every 2 hr which changed to on demand or approximately every 2-3 hr or 8-9 feeds per 24 hr period. The FWZ infant reached 15% of BW by day 9 with 8 to 9 feeds per 24 hr period. Consumption increased to 22% by day 25. Number of feeds decreased to 7 on day 29 and consumption gradually dropped to 20% by day 43 and remained there until day 60. During this time the infant transitioned from “on demand” to a more consistent schedule. On day 61 number of feeds was decreased to 6 (every 4 hours) and consumption dropped to 15-10% BW for most days and remained there including the day the infant was transferred to Cleveland.
Assessment consisted of measuring fluid loss for the 8 days by weighing diapers before and after to provide total fluid out with a normal range considered to be 33-67% for total fluids out divided by total fluids in. The FWZ infant’s fluid out ranged from 35-49% with 1 outlier of 26%. Fecal color (green, yellow/mustard, brown, grey) and texture (watery, loose, mushy, smooth, lobed, hard pellets) were regularly assessed. Based on human infants, a loss of 10-15% of BW was expected with peak weight loss days 3-6 and regain to birth weight expected to take 10-14 days. For the FWZ infant peak weight loss occurred on day 3 (dropped from birth weight of 1400 g to 1330 g) and return to birth weight occurred on day 7. Compared to full term infants, premature infants are significantly more hydrated (Ursprung, personal communication, 2024). Consequently, the higher fluid loss (up to 15%) compared to up to 10% for full term. The Fenton chart for premature female infants was used to assess growth (Fenton, 2013). Considering gorillas grow faster than humans (Thompson, 2021), this chart may have been a minimum for a gorilla. The FWZ infant maintained appropriate growth according to this chart (Figure 1). Growth was also assessed with comparison to the Cleveland premature gorilla and hand-raised full term gorillas (Figure 2). Detailed data were not found for wild or parent-reared infants. The FWZ infant for the first 70 days (data on Cleveland infant went to 70 days) gained at a rate of 35 g/d, similar to the growth rate of the Cleveland premature infant, 32 g/d, while both exceeded the average growth rate of the hand-reared infants, 18 g/d ± 6.2 (n=11). Though the growth rate was greater than humans and hand-raised full term infants, body condition was not considered over conditioned. The FWZ infant reached developmental milestones similar to parent-reared infants sooner than the Cleveland premature infant.
Challenges with raising a premature infant were not nutritional but significant. Initially, finding an appropriate bottle and nipple was difficult. FWZ had success with Dr. Brown’s preemie bottles and nipples with different flow rates. FWZ utilized a children’s speech therapist to assist with feeding/understanding nonverbal cues to nursing, dealing with a premature infant’s inability to breath and nurse at the same time, and with positioning the infant. Once consistent nursing and weight gain was established, husbandry was altered to mimic gorilla behavior. This included wearing a coat to mimic gorilla hair, holding the infant similar to a gorilla mother, as well as holding the infant around the clock. Considering every attempt was made to reintroduce the infant to her mother and then encourage another female to become a surrogate, significant training was done with an extender bottle that facilitate feeding the infant through the mesh of the cage front.
WardGorillaHandRearZN2025HRLightning.pdf 406 KB
