Effects of two protein sources and energy level of diet on the performance of young Marchigiana bulls. 1. Infra vitam performance and carcass quality

The aim of this trial was to evaluate the influence of two protein sources and the energy levels of the diet on growth performance and carcass quality of young Marchigiana bulls. Eighteen weaned young bulls (129 d of age) were equally divided into three groups. Until the slaughter weight (620 kg) was achieved two groups were fed diets with the same protein and energy concentrations, but differing in protein sources (faba bean-FB vs soya bean meal s.e.-SB), and the last group was fed high-energy diets (HE) with both protein sources in the concentrates. Body weight, daily weight gain and biological efficiency of growth at different ages and periods, and feed conversion indexes, were calculated from individual growth curves. Beginning at 180 d of age Group HE showed always significantly (P<0.01) higher body weight and daily weight gain than groups FB and SB. Moreover, group HE reached the slaughter weight and conformation earlier than the other two groups (500 vs 540 d, respectively). The protein sources affected the growth only in the first phase after weaning (body weight at 180 d: 173 vs 186 kg for groups FB and SB, respectively; P<0.01). The highest energy diets appreciably improved growing rate, but worsened feed conversion indexes. Animal and carcass measurements were not influenced either by energy intake or by dietary protein source. Group HE showed the lowest incidence of long bones (6.2 vs 6.7 vs 5.8% of cold carcass for FB, SB and HE groups respectively; P<0.01) and the highest percentage of fat (5.1 vs 4.7 vs 7.1% of cold carcass, for FB, SB and HE groups respectively; P<0.01). As respects the protein sources, only the incidence of long bones resulted significantly different between FB and SB groups (6.2 vs 6.7% of cold carcass, respectively; P<0.05). These data demonstrate that faba beans could be used as alternative sources to soya bean meal s.e., as it did not influence growth rate and feed conversion indexes in the entire experimental period. Nevertheless, immediately after weaning, the association of faba beans with another protein source richer in rumen undegradable protein would be preferable. Moreover the utilisation of high energy feeding planes could improve the growth dynamics of young Marchigiana bulls, although in the final phase it may be suitable to reduce the energy intake in order to decrease fat deposition.