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

Abstract

The domestic horse is used as a nutritional model for rhinoceros maintained under human care. The validity of this model for browsing rhinoceros has 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 nutrition knowledge is used to assess supplements for rhinoceros; therefore, the second objective was to evaluate the domestic horse model for black rhinoceros fermentation and compare fermentation responses to GSE using a continuous single-flow in vitro culture system. Two replicated continuous culture experiments were conducted using horse and black rhinoceros faeces 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 hindgut microflora nutrient digestibility and fermentation responses to GSE did not differ, and results supported equine fermentation as an adequate model for microbial fermentation in the black rhinoceros. Interpretation of these results is limited to hindgut fermentation and further research is needed to compare foregut digestibility and nutrient absorption between these two species. Supplementation of GSE in black rhinoceros diets up to 4% is unlikely to adversely affect hindgut nutrient digestibility or microbial viability and fermentation.

Species and individual rhinoceros affect the bacterial communities, metabolites, and nutrient composition in faeces from Southern black rhinoceros (Diceros bicornis minor) and Southern white rhinoceros (Ceratotherium simum simum) under managed care

“…Equine fermentation has been used as an adequate model for BR microbial fermentation (Huntley et al, 2017 ). Previous work in horses demonstrated an increase in cecal bacterial diversity from horses consuming hay versus those diets with increased starch content (Hansen et al, 2015 ).…”

Practical Management of Iron Overload Disorder (IOD) in Black Rhinoceros (BR; Diceros bicornis)

“…A number of natural oral chelators have had preliminary evaluations with mixed results. Grape pomace has been tested as a form of natural tannin for iron-binding in black rhinos, but other minerals (Cu and Zn) appeared to be impacted in terms of serum values and digestibility, though inconclusive statistically [137,138]. Also, depending on the origin of the pomace, iron content varied greatly and contributed iron to the diet.…”

Expanded catalogue of metagenome-assembled genomes reveals resistome characteristics and athletic performance-associated microbes in horse

“…Horses have been employed as a model system for investigating digestion in herbivores with hindgut fermentation, which include donkey, zebra, rhinoceros, and elephant, and for studying ruminant caecal digestion [ 4 , 5 ]. The intestinal tract of horses contains a large number of symbiotic bacteria, fungi, archaea, protozoa, and virus [ 6 ], which provide animals with the hydrolytic enzymes that convert carbohydrates into energy by fibre fermentation [ 7 , 8 ].…”