Methionine supplementation of a diet based on horse-bean : effects on growth rate, slaughter rate and carcass composition in rabbit

Abstract

Five groups of twenty rabbits received from 5 to 11 weeks of age, one of 5 diets based on horse bean (Ascott variety, 36 %) supplemented or not with pure dl-meth1onine in order to obtain the following final levels of sulphur amino acids (SAA) : 0.37 % - 0.47 % - 0.57 % - 0.62 % or 0.67 %. On average the diet's protein content was 16.9% as fed, and the crude fiber level 12.1 %. Nutrients digestibility was measured with the 0.62 % SAA diet: nitrogen 70.3 %, crude fiber 18.3 %, energy 68,7 %. The digestible energy content was 2670 kcal/kg as fed. The lowest level of SAA (0.37%) reduced significatively the daily growth rate (33.7 g/day). The highest one was observed with 0.62 % SAA: 40.8 g/day, but differences between the 0.47 % to 0.67 % SAA dlets were not significant. The feed efficiency was not affected by the diet's SAA level. The slaughter rate increased with the diet's SAA content, from 58.2 % to 60.1 %. As proportions of the whole carcass, liver, hind legs or kidney fat weights were not affected by the diet's SAA content. The same was observed for the hind leg meat-to-bone ratio. According to the authors, the SAA mínimum level is 0.47 % and the optimum 0.62 %, for diets with the digestible energy and protein contents employed in this expenment.