Mineral absorption in the black rhinoceros (Diceros bicornis) as compared with the domestic horse.

The research article explores the differences in mineral absorption between black rhinoceroses and domestic horses, to determine if dietary recommendations for horses can also meet the nutritional requirements of rhinoceroses. The study reveals notable variances in how these animals process certain minerals.

Methodology and Sample

• The researchers conducted 32 feeding trials using eight black rhinoceroses from three zoos. They also drew from data compiled from three unpublished studies.
• The focus was predominantly on the absorption of macro- and microminerals from the feeds, analyzing for minerals such as calcium, phosphorus, magnesium, sodium, potassium, iron, manganese, copper, zinc, and cobalt.
• The trial involved a total fecal collection to measure absorption rates.

Mineral Absorption in Black Rhinoceroses and Horses

• The study found higher apparent absorption (aA) of calcium and magnesium in rhinoceroses compared to horses – a phenomenon attributed to a higher ‘true’ absorption in rhinoceroses.
• Lower absorption rates were seen for sodium and potassium in rhinoceroses, and this was attributed to higher endogenous fecal losses.
• For microminerals, the absorption patterns in both rhinoceroses and horses displayed no marked differences.
• Interestingly, iron absorption in rhinoceroses showed no discernable variance with or without tannin supplementation in the diet.

Implications of Findings

• The observed higher absorption efficiency of divalent cations (calcium and magnesium) in rhinoceroses is hypothesized to be an adaptation to their natural diets that have high calcium to phosphorus ratios (approximately 14:1).
• The higher fecal losses of sodium and potassium could be linked to higher fecal bulk per dry matter intake in rhinoceroses – the result of a general lower digestive efficiency when compared to horses.
• The tested zoo diets were found deficient in copper, manganese, or zinc in several instances, and most had excess levels of iron relative to horse requirements.

Conclusions

• The study concludes that substantial differences in mineral absorption exist, even between species with similar digestive anatomy.
• Variables like calcium absorption might differ between hindgut fermenters based on the calcium-to-phosphorus ratio in their natural diets.
• Sodium could be a limiting factor in the ecology of free-ranging rhinoceroses, and it was also found that moderate tannin doses do not markedly affect mineral absorption.
• Additionally, the findings emphasise the need for well-balanced diet plans for captive animals that ensure adequate mineral inclusions and avoid excessive levels.