Comparison of the chemical composition of the diet of three free-ranging black rhinoceros (Diceros bicornis) populations with zoo diets [abstract only]

We documented seasonal changes in the dietary chemical contents of three free-ranging
black rhino populations showing contrasting reproduction performances in three different
habitats. The study was carried out in the Waterberg Plateau Park in North Central
Namibia, Tswalu Kalahari Reserve in the Northern Cape, South Africa and in the Great
Fish River Reserve in the Eastern Cape, South Africa from May to November. Browse
species contributing 80% of the dry mass of the diet were analysed for NDF, ADF, ADL,
crude protein, condensed tannins and minerals. We compared the dry season average
dietary contents and monthly average ranges of these chemical components with dietary
averages and ranges reported for zoo diets. Captive diets are low in cell wall constituents(NDF and ADF) and extremely low in indigestible fibre (ADL) compared to free-ranging
diets. Dietary iron content in captive diets is 2 to 5 times higher than in free-ranging diets.
Phosphorus, zinc and copper are in excess in captive diets compared to free-ranging diets.
Therefore we recommend that special attention should be given to the type and proportion
of roughage when formulating diets for black rhinos, and the addition of browse should be
encouraged whenever possible to reduce overall digestibility. Iron levels in captive diets
should be reduced to levels similar to those observed for free-ranging diets. The results of
this study also raise the question of the adequacy of the horse model for minerals and
protein requirements for browsing rhinos as the average dietary contents of these nutrients
in the diet of a high performance population are below or close to the maintenance
requirements for horses. Metabolic allometry needs to be taken into consideration when
estimating requirements for black rhinos.