Feeding growing rabbits with low dietary protein level and high soluble fibre to starch ratio

To evaluate the effect of decreasing dietary protein and replacing starch with soluble fibre on digestive physiology and performance, 246 hybrid rabbits (782±53 g LW) weaned at 33 d of age were divided into six groups and fed ad libitum until slaughter (76 d) six iso-ADF diets. The diets varied according to two protein levels (15.2% and 16.2%) combined with three soluble fibre to starch ratios (0.2, 0.6 and 1.5) obtained by replacing starch (20.9 to 9.1%) with soluble fibre (4.8% to 13.6%). Data were submitted to ANOVA by GLM procedure of SAS. The diet with 16.2% CP and 0.2 soluble fibre to starch ratio determined the highest mortality rate (17.1 vs 1.7%; P<0.001) compared to the other diets. When dietary CP increased, the digestibility of dry matter (61.5% to 62.6%), gross energy (62.0% to 63.0%) and aNDF (29.8% to 32.3%) significantly (0.001<P<0.10) raised and caecal volatile fatty acids (VFA) increased (59.0 to 68.4 mmol/L; P=0.01). Growth performance and slaughter traits were not affected by the protein level. When soluble fibre to starch ratio raised, the digestibility of dry matter and gross energy did not change, while the digestibility of aNDF (26.4 to 35.2%) and ADF (16.7 to 26.7%) linearly increased (P<0.001). Caecal VFA concentration (56.0 to 67.3 mmol/L) and acetate proportion linearly increased, while butyrate and valerate proportions decreased (0.01<P<0.05). Growth performance was similar among groups, while at slaughter the proportion of the gastro-intestinal tract linearly increased (17.7 to 18.4%; P<0.01) without affecting dressing percentage. Meat pH linearly decreased and L*, a* and b* colour indexes increased (0.01<P<0.05). In conclusion, feeding rabbits with low-protein and high-soluble fibre to starch ratio diets reduced mortality, improved digestive efficiency and intestinal environment without affecting growth performance.