Effects of the ratio of silage to concentrates in the diet on the performance and carcass composition of continental bulls

A total of 45 continental bulls (1/2 Blonde d'Aquitaine/3/8 Charolais) were used in a continuous design randomized-block experiment, to examine the ef fects of the ratio of silage to concentrates in the diet on growth and carc ass parameters. The proportions of concentrates in the five diets were 0.26 , 0.40, 0.55, 0.68 and 0.75 (DM basis). The basal diet was grass silage wit h D value 730 g/kg and ammonia nitrogen per unit total nitrogen 86 g/kg. Th e mean initial and final live weights were 467 and 651 kg respectively, wit h a mean carcass weight of 384 kg. The digestibility of energy was not affe cted by the proportion of concentrates in the diet. The rates of live weigh t, carcass and separable lean tissue gain tended to reach a plateau at the higher concentrate proportions, while the rate of separable fat tissue gain increased linearly with increase in concentrate proportion. The separable lean content of the carcass was linearly and negatively related to the prop ortion of concentrates, with a predicted decrease of 10 g/kg for an increas e in concentrate proportion of 0.16. Separable fat content was also linearl y related to the proportion of concentrates, with a predicted increase of 1 0 g/kg for each 0.196 increase in proportion of concentrates. The absence o f any effect of concentrate proportion on the content of saleable meat in t he carcass was considered to reflect the high growth potential of the anima ls. An important conclusion was that 0.99 of the asymptote value for lean t issue gain was attained at a concentrate proportion of 0.52 and that 0.95 o f the maximum rate of gain was obtained at the relatively low concentrate p roportion of 0.39, therefore indicating that finishing bulls of this type c an perform to a high level on diets which are predominately based on grass silage.