Etude du besoin en lysine du lapin en croissance en relation avec la concentration énergétique de l'aliment

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Abstract
A total of 96 Californian rabbits of both sexes and aged 5 wk were allocated to 6 treatments corresponding to a factorial design including 3 lysine levels (0.45, 0.60, 0.75%) and 2 crude fiber levels (10.0, 17.2%). Their growth performance was studied during 35 days and the carcass yield measured in half of the animals at slaughter. N retention and the apparent digestibility and metabolic utilization were determined in the other 1/2 of the animals (8/treatment). Increase in the crude fiber content of the diet (obtained by replacing part of the dietary starch by purified crude fiber) led to a lowering (7.5%) of the digestible energy content of the diets, but did not change the apparent digestibility of protein. At the 2 energy concentrations, the addition of supplementary lysine improved growth, feed efficiency, N balance and N retention coefficient. For the diets with the lowest energy content, these improvements only occurred between lysine levels ranging from 0.45-0.60%, while they were also observed at lysine levels ranging from 0.60-0.75% in the case of the diets with the highest energy content. The lysine requirement of the rabbit varies with the digestible energy concentration of the diet. A more accurate definition of this requirement should be made in relation to the digestible energy level of the diet. It then represents around 2.4 g lysine/1000 kcal digestible energy. Increase in the crude fiber level reduced the carcass yield by 1.2, 1.6 points, while a rise in the dietary lysine level seemed to strongly enhance the loss of water during shrinkage.