Replacement of digestible fibre by starch in the diet of the growing rabbit. I. Effects on digestion, rate of passage and retention of nutrients

Abstract

The effects of digestible fibre replacement (25 to 15%) by starch (12 to 23%), were studied on rabbit digestion with four diets (A 12 to A24) having a similar level of lignoccllulose (ADF, 18%). Faecal digestibility, retention of nutrients and rate of passage were measured on four groups of 12 young rabbits fed the four diets ad libitum from weaning to slaughter (72 d). Intake, weight gain, and feed conversion were not significantly different among the 4 treatments (mean 102.4 g·d-1, 34.0 g-d-1,3.02 respectively). Despite a 100% increase in the starch level between A12 and A24, the digestibility of organic matter and energy were similar (mean 65.5 and 63.7% respectively). Energy or protein retention were not significantly affected by treatments (mean 28.4 and 13.6% respectively). With a reduction of the supply in digestible Obre, overall fibre digestibility (NDF) was logically reduced (-10 units), particularly for the uronic acid fractions (71 to 44% respectively for A12 and A24). Consequently the quantity of degraded NDF (period 28-72 d) decreased from 13.7 to 8.1 g·d-1 for the A12 to A24 diets, while it doubled for starch (12.5 vs. 23.1 g·d-1). Whole tract mean retention time for the paniculate phase increased by 2 h (P = 0.06) for the A12 to A24 diets, while it increased by 4 h (P< 0.01) for the liquid phase. Caecal retention time of fine particles was more affected (+6 h) than that of large panicles (+2 h). In conclusion, digestible fibre replacement by starch did not change the digestive efficiency of the rabbit, but slowered the passage rate.