Milk nutrient comparison across three species of rhinocerous: Ceratotherium simum, Diceros bicornis, and Rhinoceros unicornis

Citation

Shinnerl HE, Bornbusch SL, Thacher P, Kendrick EL, Maslanka M, and Power ML. 2025. Milk nutrient comparison across three species of rhinocerous: Ceratotherium simum, Diceros bicornis, and Rhinoceros unicornis. 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

Introduction

Mammals are born obligate lactivores. Neonates are wholly reliant on their mother’s milk to meet their nutritional requirements. Eco-evolutionary factors have shaped mammal milk over time, with each species adapting to their unique life history, diet, and lactation strategies. The Rhinocerotidae family contains five species of extant rhinoceroses, three of which are represented in North American zoos: the Southern White Rhino (Ceratotherium simum; SWR), Black Rhino (Diceros bicornis; BR), and the Greater One-Horned Rhino (Rhinoceros unicornis; GOHR). Milk samples from captive animals are a valuable resource to better understand eco-evolutionary differences between species, and how to better advise the development of milk replacers, both in zoos and in country rehabilitation centers.

Materials and Methods

Samples from the Smithsonian’s National Zoo Milk Repository were analyzed for total fat, total sugar, crude protein (CP), ash, dry matter (DM), calcium, and phosphorus using established AOAC methods. Estimated gross energy (GE) was calculated using the following factors: 3.95 kcal/g for sugar, 9.11 kcal/g for fat and 5.86 kcal/g for crude protein (Perrin, 1958). These values for GE have been validated at the Smithsonian’s National Zoo Nutrition Laboratory using bomb calorimetry for multiple species (Wenker et al., 2019; Himschoot et al., 2021). Samples were collected from multiple females for each species and across multiple days post parturition (dpp): SWR: n = 76, median dpp 224.5, GOHR: n = 41, median dpp 333, and BR: n = 10, median dpp 68.5.

Results and Discussion

The macronutrient profile for the milk of each species is reported in Table 1. Significant statistical differences were observed between the sugar, protein, calcium, and phosphorus content of SWR milk, GOHR milk, and BR milk (P < 0.05). No differences were observed between species for GE, fat, or DM. The only nutrient that changed over time was calcium in SWR milk, which significantly increased throughout lactation (P < 0.05). All milk samples meet the typical rhino milk profile: low dry matter, low protein, very low fat, and moderate-to-high sugar content, when considered on an as-is basis.

When considered on an energy basis, about 60% of milk GE for BR and GOHR comes from sugar, while in the SWR almost 70% comes from sugar. Protein, while “low” when expressed as a percent of the milk, contributes about 20% of GE for SWR, and about 25% of GE for GOHR and BR (Table 1). This proportion of milk GE from protein is comparable to or higher than values for Asian and African elephants (Himschoot et al., 2021).

It is not clear if the statistical differences in macronutrient composition are biologically significant. Differences seen between species may be a result of their nutritional ecology, SWR are grazers whereas BR are considered browsers. However, the number of samples per species, and their average age may also be impacting results. For example, only 10 BR milk samples were analyzed with an average sample age of 124 dpp, median of 68.5 dpp. The apparent higher proportion of GE from protein in GOHR and BR compared to SWR would be consistent with SWR calves having a slower growth rate. This should be examined, and, if true, would be indicative of GOHR and BR calves needing a milk replacer in protein than would than SWR calves.

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