Black rhinoceros (Diceros bicornis) and domestic horse (Equus caballus) hindgut microflora demonstrate similar fermentation responses to grape seed extract supplementation in vitro

Summary The domestic horse is used as a nutritional model for rhinocerosmaintained under human care. The validity of this model for browsing rhinoceroshas been questioned due to high prevalence of iron overload disorder(IOD) in captive black rhinoceros(Diceros bicornis), which is associated with high morbidity and mortality. Iron chelators, such as tannins, are under investigation as dietary supplements to ameliorate or prevent IOD in prone species. Polyphenolic compounds variably affect microbial fermentation, so the first objective of this experiment was to evaluate the effects of grape seed extract(GSE; a concentrated source of condensed tannins; CT) on black rhinoceros hindgut fermentation. Equine nutritionknowledge is used to assess supplements for rhinoceros; therefore, the second objective was to evaluate the domestic horse model for black rhinoceros fermentationand compare fermentationresponses to GSE using a continuous single-flow in vitro culture system. Two replicated continuous culture experiments were conducted using horse and black rhinocerosfaeces as inoculum sources comparing four diets with increasing GSE inclusion (0.0%, 1.3%, 2.7% and 4.0% of diet dry matter). Diet and GSE polyphenolic compositions were determined, and sodium sulphite effect on neutral detergent fibre extraction of CT-containing forages was tested. Increasing GSE inclusion stimulated microbial growth and fermentation, and proportionally increased diet CT concentration and iron-binding capacity. Horse and black rhinoceros hindgutmicroflora nutrient digestibility and fermentationresponses to GSE did not differ, and results supported equine fermentationas an adequate model for microbial fermentationin the black rhinoceros. Interpretation of these results is limited to hindgut fermentationand further research is needed to compare foregutdigestibility and nutrient absorption between these two species. Supplementation of GSE in black rhinocerosdiets up to 4% is unlikely to adversely affect hindgutnutrient digestibility or microbial viability and fermentation.