Studies on digestive physiology and feed digestibilities in captive Indian rhinoceros (Rhinoceros unicornis).
Authors: Clauss M, Polster C, Kienzle E, Wiesner H, Baumgartner K, von Houwald F, Ortmann S, Streich W J, Dierenfeld E S
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary: Digestive Physiology in Indian Rhinoceroses Researchers from four zoos studied how eleven Indian rhinoceroses digest and process feed by conducting intake, digestibility and faecal marker studies comparing a conventional zoo diet (roughage plus concentrates) against roughage alone, with hay and silage sources varying between facilities. Dry matter intake averaged 0.8–1.3% of body weight on the mixed ration and 0.5–1.2% on roughage only, whilst digestibility coefficients and endogenous nitrogen losses closely paralleled those documented in horses despite the rhinoceroses' vastly greater body mass. Notably, mean gastrointestinal transit times were exceptionally prolonged—42 hours for fluid and 61 hours for particles—the longest reported for any monogastric ungulate using these marker systems, yet faecal volatile fatty acid profiles, lactate concentrations and pH remained similar to equine values. These findings validate the horse as a practical reference model for formulating Indian rhinoceros diets in captive settings, though the mechanistic basis for equivalent digestive outputs despite dramatically different retention times and body weight warrants further investigation. Equine professionals working with zoo nutrition programmes can therefore apply established equine dietary principles to rhinoceros management with reasonable confidence, though individual variation in intake and the influence of roughage type should still be monitored carefully.
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Practical Takeaways
- •While this study concerns rhinoceros nutrition, the finding that digestive parameters parallel horses despite vastly different body sizes suggests equine nutritional models may have broader application to large monogastric herbivores than previously recognized
- •The exceptionally long gastrointestinal transit times in rhinoceros (42-61 hours) compared to horses indicate that body size influences digestion differently than current models predict, warranting caution when extrapolating feeding strategies across species
- •Zoo nutritionists and exotic animal practitioners can reference equine digestibility coefficients and endogenous loss data when formulating Indian rhinoceros diets, but should verify outcomes with captive animals given the unexplained physiological similarities
Key Findings
- •Dry matter intake ranged 0.8-1.3% of body weight on mixed ration and 0.5-1.2% on roughage-only ration across 11 Indian rhinoceroses
- •Digestibility coefficients and endogenous losses in Indian rhinoceroses were similar to horses despite enormous differences in body weight
- •Mean retention times were 42 hours for fluids and 61 hours for particles, the longest ever recorded in a monogastric ungulate using these markers
- •Faecal volatile fatty acids, lactate, and pH measurements showed similarity to horses, suggesting the horse is a useful model for designing Indian rhinoceros diets