Effect of dietary protein and amino acids on the performance, carcass composition and N-excretion of growing rabbits

Abstract

A total of 234 weanlings (32-day-old) were fed during 6 weeks ad libitum one of six diets, produced after progressively blending a high protein 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 protein content between 170.1 g and 137.5 g kg-1. Lysine, methionine + cystine and threonine were at 1.45 times their assumed requirement in the high protein mix to avoid deficiencies of these amino acids in the experimental 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 resulted in a significant lower growth rate and feed intake during the first 3 weeks post weaning. However, during the finishing period (last 2 weeks) weight gain on low protein diets (< 151 g kg-1) exceeded (P < 0.05) that of the high protein diets. Comparative slaughter techniques revealed a significant increased N-retention with increasing dietary protein 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 highest 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 ratio. Dressing out percentage was unaffected by the dietary treatment. The results suggest that dietary protein and amino acid levels of growing 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 performances.