Factors that inform the formulation of milk replacers for exotic mammals: biology and macronutrient content

Citation

Power ML. 2025. Factors that inform the formulation of milk replacers for exotic mammals: biology and macronutrient content. 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

All mammals, whether as adults they are carnivores, omnivores, or herbivores, begin life as lactivores. The first food of any newborn mammal should be mother’s milk. Unfortunately, that is not always possible. Neonates may be orphaned, rejected by the mother, or mother and baby may need to be given medical treatment that precludes nursing. In these instances, caregivers must prepare a milk replacer. In this talk I will summarize what is known about how aspects of the biology, ecology and lactation strategy affect the milk macronutrient composition of a species. These associations can inform the formulation of a milk replacer if data on actual macronutrient composition is lacking.

Although we cannot duplicate all the important bioactive components of mother’s milk, when formulating a milk replacer, the macronutrient content should be made to be as close to the species’ milk as is possible. Neonatal guts are immature and should not be challenged with foods far outside of the evolved milk they would normally receive. Placental mammal milks vary widely in macronutrient composition. The milks of equids and most primates are high in sugar and water and moderate or low in fat and protein. Carnivores and insectivores produce milks high in protein with low-to-moderate sugar. Marine mammals produce milks high in fat with barely any sugar. Neonatal digestive abilities have evolved to cope with their species milk and may be challenged by a milk replacer that is significantly different from mother’s milk.

Data on macronutrient composition of milk from about 200 placental mammal exists, either in the literature or in the files of the milk repository at the Smithsonian’s National Zoo and Conservation Biology Institute. Based on those data, biological factors that are associated with milk macronutrient composition include phylogeny, the evolved maternal diet, litter size, lactation strategy (e.g. nursing frequency), neonatal growth rate, and whether neonates are altricial or precocial. None by themselves are definitive, but in combination they can inform the macronutrient composition of the milk replacer.

In this talk I will summarize the associations between the known macronutrient content of the milks from a number of taxa and a set of biological factors. From these test cases strategies to enable informed “guesses” about a species milk when data are lacking can be derived.

PowerMilkReplacersZN2025S1.pdf     116 KB