Dietary neutral detergent fibre and lignin contents affect intake, digestibility and digesta retention in captive sloths (Bradypus variegatus).

We evaluated food intake, digestibility, digesta retention and digestible energy (DE) intake in four three-toed sloths (Bradypus variegatus, body mass 2.86 ± 0.10 kg) fed two leaf-based diets containing different neutral detergent fibre (NDF) and lignin contents. Total dry matter intake (DMI), and intake in relation to body mass and metabolic body weight were higher for the mixed diet with lower NDF content based on Pterondon sp. + Inga sp. (47 g day , 16 g kg  day and 21 g kg  day ) compared to the treatment with higher content of NDF from only Cecropia pachystachya leaves (37 g day , 14 g kg  day and 18 g kg  day ). The digestibility of dry matter (dDM) and neutral detergent fibre (dNDF) were higher in the mixed diet (60% and 61% respectively). There was a higher supply of DE and metabolisable energy (ME) on the mixed diet, at 221 and 199 kJ kg  day , meeting the average energy requirement of 185 kJ ME kg  day ME estimated for sloths in this study. In contrast, the diet with C. pachystachya generated a deficit of 31 kJ ME kg  day . There was a correlation between DMI and dNDF (r  = 0.89), and between dNDF and dDM (r  = 0.98) across treatments. The mean retention times for a liquid and a particle marker were lower on the mixed diet with the higher intake at 133 h (passage rate = 0.75% h ) and 181 h (0.55% h ), and longer on the single-species diet with lower intake at 204 h (0.49% h ) and 261 h (0.38% h ). The results suggest that it may be beneficial for sloths to be offered a variety of browse from which they can choose low-NDF components. Further, we suggest that these sloths perform 'digesta washing' to increase the microbial yield in the stomach to maximise the digestion of NDF and dry matter.