EFFECT OF DIETARY-PROTEIN AND AMINO-ACIDS ON THE PERFORMANCE, CARCASSCOMPOSITION AND N-EXCRETION OF GROWING RABBITS

A total of 234 weanlings (32-day-old) were fed during 6 weeks ad libit um one of six diets, produced after progressively blending a high prot ein mixture with a low protein mixture, in order to obtain a series of six iso-energetic (10.4 MJ DE/kg) diets with linear decreasing protei n content between 170.1 g and 137.5 g kg(-1). Lysine, methionine + cys tine and threonine were at 1.45 times their assumed requirement in the high protein mix to avoid deficiencies of these amino acids in the ex perimental diets. The significant interaction (P < 0.001) between type of diet and weekly weight gain demonstrated an age-dependent response to the dietary protein content, A protein level below 157 g kg(-1) re sulted in a significant lower growth rate and feed intake during the f irst 3 weeks post weaning However, during the finishing period (last 2 weeks) weight gain on low protein diets (< 151 g kg exceeded (P < 0.0 5) that of the high protein diets. Comparative slaughter techniques re vealed a significant increased N-retention with increasing dietary pro tein dilution (from 33.9 to 41.3% of intake). N-excretion was reduced by 38% on the lowest protein diet compared to the rabbits fed the high est protein diet. However, their growth rate was 9% lower. Empty body composition showed a significant increased fat content as the protein content of the diet decreased related to the changed protein-energy ra tio. Dressing out percentage was unaffected by the dietary treatment. The results suggest that dietary protein and amino acid levels of grow ing rabbits have to be considered into different age periods, in order to match them better with the requirements. An important reduction of the N-excretion could then be achieved without altering the performan ces.