A Comparison of Milk Macronutrient Composition From Domestic and Exotic Species Classified in the Order Perissodactyla

Archived and donated perissodactyla milk samples (n = 209) from 8 domestic horses (Equus caballus), 13 rhinoceroses (representing three species: Diceros bicornis, Ceratotherium simum, Rhinoceros unicornis), 5 tapirs (representing two species: Tapirus bairdii, Tapirus indicus), and 16 wild equids (representing 6 species: Equus ferus przewalskii, Equus grevyi, Equus quagga, Equus zebra, Equus africanus somaliensis, Equus asinus) were collected from different institutions (n = 16). These milk samples ranged from 3 to 200 days post parturition. Milk samples were analyzed at the Smithsonian's National Zoo and Conservation Biology Institute Nutrition Laboratory for major macronutrients: ash, crude protein (CP), dry matter (DM), crude fat, sugar, and gross energy (GE). Analysis of variance (ANOVA) and Tukey post hoc tests were used to compare milk values among both Perissodactyla species and families (Equidae, Rhinocerotidae, and Tapiridae). Overall, there was little variation of milk macronutrient compositions within perissodactyla families besides the differences between black and white rhinos observed (black rhinoceros: CP = 2.81%, fat = 2.10%, sugar = 6.06%, ash = 0.36%, DM = 11.73%, GE = 0.59 kcal/g, white rhinoceros: CP = 1.16%, fat = 0.42%, sugar = 6.47%, ash = 0.23%, DM = 8.96%, GE = 0.36 kcal/g); however, there were significant differences when comparing among families. Large differences (p < 0.05) in the CP content between Tapiridae and Equidae milk were observed (tapir: CP = 5.93%, fat = 2.57%, sugar = 4.62%, ash = 0.68%, DM = 15.09%, GE = 0.75 kcal/g, domestic horse: CP = 2.25%, fat = 1.22%, sugar = 6.35%, ash = 0.38%, DM = 11.04%, GE = 0.50 kcal/g). These findings indicate that domestic equine milk is an insufficient substitute for tapirs, but could be used for rhinoceroses. This result is likely to have a high impact on emerging Perissodactyla breeding and conservation programs with a strong need for milk formulas and replacements.