Digestive physiology of captive capybara (Hydrochoerus hydrochaeris).

Abstract

The capybara (Hydrochoerus hydrochaeris), the largest living rodent, probably has a mucus-trap colonic separation mechanism. To test this hypothesis, we measured the mean retention time of a solute marker (MRTSolute ), 2\u2009mm (MRT2\u2009mm ), 10\u2009mm (MRT10\u2009mm ), and 20\u2009mm (MRT20\u2009mm ) particle markers and nutrient digestibility in adult captive capybaras (27-52\u2009kg body mass (BM), 2-11 yr). In addition, total gut fill and the selectivity factor (MRTSolute /MRT2\u2009mm ) were calculated, and mean faecal particle size and metabolic fecal nitrogen of captive capybaras were compared to those of free-ranging specimens. Finally, we also measured methane production in one animal. The MRT2\u2009mm (29.2\u2009±\u20098.2\u2009hr) was different (p\u2009<\u20090.01) from MRTSolute (37.0\u2009±\u200913.1\u2009hr), MRT10\u2009mm (36.5\u2009±\u20098.2\u2009hr), and MRT20\u2009mm (35.1\u2009±\u20099.6\u2009hr). The selectivity factor (1.26\u2009±\u20090.30) was in the range considered typical for a mucus-trap colonic separation mechanism. The estimated total gut fill was 1.50\u2009±\u20090.37% and 1.73\u2009±\u20090.25% of BM calculated from the results of the 2-mm and 10-mm particle markers, respectively. The CH4 emission was 13.7 L/day. Captive capybaras had greater mean fecal particle size (0.44\u2009±\u20090.06 vs. 0.29\u2009±\u20090.05\u2009mm, p\u2009<\u20090.001) and metabolic fecal nitrogen (65.5\u2009±\u20093.91 vs. 46.8\u2009±\u200910.5% of fecal nitrogen, p\u2009<\u20090.001) than free-ranging capybaras. Organic matter digestibility decreased less steeply with increasing dietary crude fiber content in capybaras as compared to published data from rabbits or guinea pigs. Accordingly, the digestive physiology of the capybara is characterized by a comparatively high fiber digestibility, with a mucus-trap colonic separation mechanism, allowing capybaras to thrive on forage-only diets.