Digestive physiology, metabolism and methane production ofcaptive Linné's two-toed sloths (Choloepus didactylus).

Abstract

Sloths are renowned for their low metabolic rate, low food intake and low defecation frequency. We investigated factors of digestive physiology and energy metabolism in four captive individuals (mean body mass 10.0±SD 3.7kg) of a hitherto mostly unstudied sloth species, Linné's two-toed sloth (Choloepus didactylus), in a 2-week digestion recording and 23-h respiration experiment on animals fed a standard zoo diet of vegetables and starchy components. Dry matter intake, defecation frequency and particle mean retention time (MRT) in the gastrointestinal tract (GIT) were 12±3g/(kg(0.75) day), once every 5days and >140h in three individuals, but 53g/(kg(0.75) day), daily and 82h in one individual that was apparently compensating for a period of weight loss prior to the experiment. In all animals, solute marker was eliminated at a faster rate than the particle marker, indicating 'digesta washing' in the sloths' GIT. The overall metabolic rate calculated from oxygen consumption matched the metabolisable energy intake in three individuals [173±22 vs. 168±44 kJ/(kg(0.75) day)] but not in the fourth one [225 vs. 698 kJ/(kg(0.75) day)], supporting the interpretation that this animal was replenishing body stores. In spite of the low food intake and the low-fibre diet (209±26g neutral detergent fibre/kg dry matter), methane production was rather high accounting for 9.4±0.8% of gross energy intake (2.7% in the fourth individual), which exceeded literature data for ruminants on forage-only diets. These results corroborate literature reports on low intake, low defecation frequency, low metabolic rate and long MRT in other sloth species. The long MRT is probably responsible for the comparatively high methane production, providing more opportunity for methanogenic archaea than in other non-ruminant mammals to produce significant amounts of methane.