Mineral absorption in the black rhinoceros (Diceros bicornis) as compared with the domestic horse.
Authors: Clauss M, Castell J C, Kienzle E, Schramel P, Dierenfeld E S, Flach E J, Behlert O, Streich W J, Hummel J, Hatt J-M
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary: Mineral Absorption in Black Rhinoceroses versus Domestic Horses Researchers from multiple institutions conducted 32 controlled feeding trials with total faecal collection across eight black rhinoceroses, supplemented by data from 18 additional trials, to determine whether equine mineral recommendations could safely guide rhinoceros nutrition in captive settings. Using standard digestibility methodology, they measured apparent absorption coefficients for ten macro- and microminerals and compared these with established equine data, hypothesising that differences in natural diet composition—particularly the exceptionally high calcium-to-phosphorus ratio (14:1) in wild black rhinoceros forage—would influence mineral utilisation. Rhinoceroses demonstrated significantly higher absorption of calcium and magnesium but lower sodium and potassium retention than horses, likely reflecting adaptation to their high-calcium natural diet and generally lower overall digestive efficiency; critically, multiple zoological diets assessed were deficient in copper, manganese and zinc whilst containing excessive iron relative to equine standards. For equine professionals involved in exotic animal care or nutritional consultation, these findings underscore that hindgut fermenters with divergent evolutionary feeding patterns cannot be assumed to process minerals identically, and that blanket application of equine mineral recommendations to rhinoceroses risks both deficiency and toxicity, particularly for trace minerals where captive diets often deviate substantially from wild forage composition.
Read the full abstract on PubMed
Practical Takeaways
- •Horse mineral recommendations should not be directly applied to captive black rhinoceroses without species-specific adjustments, particularly for divalent cations
- •Formulate zoo diets with attention to species-specific mineral absorption patterns and natural dietary mineral ratios rather than extrapolating from equine nutritional guidelines
- •Monitor Cu, Mn, Zn, and Fe levels carefully in captive rhinoceros diets—deficiencies and excesses are common when using equine-based feeding standards
Key Findings
- •Black rhinoceroses showed significantly higher apparent absorption coefficients for Ca and Mg compared to domestic horses, attributed to higher true absorption of divalent cations
- •Rhinoceroses demonstrated lower apparent absorption of Na and K due to higher endogenous faecal losses, possibly related to lower overall digestive efficiency
- •High dietary Ca:P ratio (14:1) in natural rhinoceros diet appears to drive enhanced Ca absorption as an adaptive mechanism to maintain P availability
- •Multiple zoo diets were deficient in Cu, Mn, or Zn and contained excessive Fe levels; tannin supplementation did not markedly influence mineral absorption patterns