Henry, B. A., Power, M. L., Maslanka, M. T. et al. 2022. Challenges of devising a milk recipe in a hand‐reared hippopotamus (Hippopotamus amphibius). Zoo Biology 41(4), 360-364.

In January 2017, a Nile hippopotamus (Hippopotamus amphibious) was born approximately six weeks premature at the Cincinnati Zoo & Botanical Garden. Due to the calf's weakened condition and lack of interest from the dam, management at the zoo made the decision to hand-rear the calf. Limited published information was available on hand-rearing this species of hippopotamus (hippo). To devise a nutritionally appropriate recipe, milk samples were acquired from the dam on Days 1, 3, 8, and 9 postpartum, and assayed for sugar, protein, fat, mineral, and water content using standard methods validated for multiple species of mammals at the Smithsonian National Zoo's Nutrition Science Laboratory. The sugar content stayed relatively constant (mean = 4.5%; range: 4.3%–4.7%). The fat consistently increased from 0.48% to 4.24% (mean = 2%). Excluding Day 9, the protein content gradually decreased from 9.56% to 6.39% (mean = 8%). The dry matter (DM) ranged from 14.38% to 16.72% (i.e., water content of 85.62%–83.28%), with the sum of the solids (sugar, protein, fat, and ash) averaging 98.5% of measured DM. Fat content was lower than expected but within the range of other artiodactyls. Between Days 1 and 8, the trend of decreasing protein and increasing fat was consistent with a change from colostrum to mature milk. The sharp increase in fat and protein with a decrease in sugar on Day 9 may indicate the beginning of the involution of the mammary gland due to lack of nursing stimulus. Utilizing this information, the Cincinnati Zoo was able to formulate a successful milk replacement recipe that allowed the calf to be raised through weaning to maturity.