Digestible fibre to starch ratio and protein level in diets for growing rabbits

To evaluate the effect of digestible fibre (DF) to starch ratio (0.8, 1.5, and 2.8) and protein level (15% and 16%) on health status, digestive physiology, growth performance, and carcass traits, 246 rabbits weaned at 33 d were fed until slaughter (75 d) six diets formulated according to a bi-factorial arrangement (3 DF to starch ratios by 2 protein levels). Growth performance and carcass quality at slaughter were not affected by treatments. Increasing DF to starch ratio did not modify dry matter digestibility (62.0% on average), while increased (P<0.001) DF digestibility (52.3 to 68.1%), stimulated caecal fermentation (total VFA: 56.0 vs 67.8 and 67.2 mmol/l; P=0.02) and changed VFA molar proportions. Increasing dietary protein increased digestibility of dry matter (P=0.02), crude protein (P<0.001) and digestible fibre (P<0.001) and increased caecal VFA production (P<0.01). The highest mortality (17.1% vs 1.5% average mortality of the other groups, P<0.001) was found in rabbits fed the diet with the lowest DF to starch ratio and the highest protein level.