Increasing Dietary Energy with Starch and Soluble Fibre and Reducing ADF at Different Protein Levels for Growing Rabbits

The effect of increasing dietary energy by increasing both starch (14% to 20%) and soluble fibre (9.6% to 11.6%) and decreasing ADF content (21% to 13%) at two crude protein levels (14% and 15%) was assessed on health, growth performance, caecal fermentative activity, gut mucosa traits, and carcass and meat quality of growing rabbits reared from 34 to 76 days of age. At weaning, 306 rabbits were divided into six groups and fed ad libitum six diets formulated according to a bi-factorial arrangement with 3 (starch+soluble fibre)/ADF ratio (L=1.2; M=1.8; H=2.8) x 2 protein levels. The contemporary increase of dietary starch and soluble fibre and the reduction of ADF linearly increased the digestibility of dry matter, energy and all nutrients, decreased feed intake and improved feed conversion (3.65 to 2.76 in rabbits fed diets L and H; P<0.001); it increased morbidity (P=0.09) but did not affect mortality due to epizootic rabbit enteropathy; at caecum, VFA production raised (52.1 to 61.9 mmol/L) and pH (5.90 to 5.67) and N ammonia lowered (4.85 to 1.93 mmol/L); the villi/crypts ratio (4.42 vs. 3.81 and 3.95 in rabbits fed diets L, M and H) decreased in a non linear mode. The decrease of the protein level did not affect growth performance, but nearly halved mortality (28.9% vs. 16.3%; P=0.01) and increased caecal pH (5.70 to 5.87; P=0.05). Weak effects of the dietary treatments were measured on carcass traits and meat quality.