Role of the dietary supplementation of arginine and valine: health status, digestibility, and performances of growing rabbits

Arginine is a semi-essential amino acid that plays an important role on protein synthesis and immune response of growing rabbits. Valine is an essential branched-chain amino acid involved in the stimulation of protein synthesis and in the reduction of structural protein catabolism. The study aimed at evaluating the effects of the dietary supplementation with synthetic L-arginine and L-valine on health status, diet digestibility, growth performance, carcass and meat quality of growing rabbits. To this aim, 336 Hyplus Grimaud crossbred rabbits of both sexes, weaned at 32 d of age, were divided into 4 experimental groups with 12 replicates (pen) each (7 rabbits/pen) fed 4 experimental diets (Diet C, not supplemented with the tested amino acids; diet A, with 0.4% L-arginine; diet V, with 0.4% L-valine; diet AV, with 0.4% L-arginine and 0.4% L-valine), offered ad libitum during the whole trial. At 73 days of age, all animals were slaughtered in a commercial slaughterhouse and 144 carcasses were selected and submitted to dissection and meat quality assessment. The supplementation of arginine and valine, individually or in combination, did not affect final live weight (2771 g on average), growth rate (49.5 g/d), feed intake (146 g/d) and feed conversion (3.00 g/g) during the trial. Nutrients digestibility was scarcely affected by the dietary treatment apart from the digestibility coefficients of NDF and ADF, which were higher in rabbits fed diet V compared to other rabbits (+17% and +21% on average, respectively; P<0.05). The health status of the animals was affected by the appearance of epizootic rabbit enteropathy, and a mortality rate equal to 13.1% on average was reached in the whole trial. The mortality rate tended to be higher in rabbits fed diet AV than in those fed diet C (16.7% vs. 10.7%; P=0.07). Slaughter weight and dressing out percentage averaged 2643 g and 61.9%, respectively, without significant differences among dietary treatments. Meat quality was not affected by valine supplementation, whereas rabbits fed the diet supplemented with arginine showed lower pH values in the biceps femoris muscles with respect to those fed the other experimental diets (P<0.01). In conclusion, under the conditions of the present study, neither growth performance nor mortality rate or carcass and meat quality were substantially improved by the dietary supplementation with synthetic arginine and valine, and then their dietary supplementation cannot be recommended.