Preliminary impacts of dietary phytate supplementation on iron and phosphorus in black rhinoceros (Diceros bicornis)

Black rhinoceroses (Diceros bicornis) under human care are susceptible to health issues associated with diet management, including iron overload disorder, hypophosphatemia, renal and gastrointestinal disorders. As browse diets for free-ranging rhinos cannot be replicated under human care, we do not understand the exact nutrient needs that optimize physiological wellness. Current recommendations under human care include supplementation of vitamin E and phosphorus and limiting bioavailable iron (Sullivan & Valdes, 2019; Sullivan et al., 2020). Inositol hexaphosphate (IP6) has been demonstrated to serve as an iron chelator, antioxidant, and anti-inflammatory reactant across species, but it is also a potential source of dietary phosphorus in hindgut-fermenting rhinos. We hypothesized diet supplementation with IP6 would have benefits including decreased iron availability and improved circulating phosphorus for black rhinos. Four male black rhinos at Disney’s Animal Kingdom® and Fort Worth Zoo (n = 2/institution), were enrolled in a randomized crossover study with two 21-d experimental periods with and without IP6 supplementation fed at 190% of the estimated horse-based phosphorus recommendation. Multiple-month washouts occurred between treatment periods and animals served as their own controls. Serum measurements collected on d0 and during d15-21 included iron biomarkers, CBC, and chemistry panels. All animals consumed 100% of IP6 offered with no change in animal health throughout the study. While iron parameters did not demonstrate changes (P > 0.3) there were numerical decreases; and serum phosphorus, shown to be protective against hemolytic crises, was increased with IP6 supplementation (P = 0.02; Table 1; Sullivan et al., 2020). Understanding the importance, optimal diet forms, and interplay of iron and phosphorus in black rhino physiology are critical to maintain a healthy sustainable population.