Feeding management of African rhinos (Ceratotherium simum, Diceros bicornis) in European zoos

White rhinos (WR, Ceratotherium simum) are grazers and black rhinos (BR, Diceros bicornis) are browsers; this difference has been related to BR being more challenging in terms of husbandry. Previous reports indicated that BR in zoos often receive diets with a higher proportion of easily digestible compounds compared to other rhino species. Additionally, BR are susceptible to iron overload disorder (IOD). We compared the feeding methods and recommendations, and sampled diets and feces of 117 WR and 82 BR across 41 European zoos. The few available data for free-ranging animals were also incorporated. The percentage of forage in the total estimated dry matter intake was 93% for WR and 77% for BR, matching fecal parameters indicating a higher diet digestibility in BR. BR received higher levels of (pelleted) compound feeds and produce than WR. Nevertheless, dietary fiber levels were similar to that reported for free-ranging specimens in both species. Zoo diets were higher in several minerals (Na, P, Cu, Zn) than natural diets. However, zoo BR received diets with similar iron content to that described in free-ranging BR diet items and fecal iron levels were not higher than those in the few samples of free-ranging BR available, suggesting that iron levels in zoo BR diets are not overly excessive. Consequently, IOD appears to be more complex, associated with iron bioavailability and possibly non-dietary causes. Grass hay was used in 100% of WR and 36% of BR (all BR facilities used lucerne hay). BR feces had levels of abrasive silica comparable to those of free-ranging WR and much higher than free-ranging BR, matching reports of excessive tooth wear in adult BR. Browse provision for BR could not be quantified but appeared low in general; no alternative forages (like sainfoin) were fed. Efforts to consistently provide high amounts of browse to BR must be increased and forage should be low in iron and abrasive silica.