Effects of mixing disbudded and horned young bulls during rearing on the post-mortem Longissimus thoracis muscle proteome

Eighty-one young Swiss cross-bred bulls, half of which were disbudded at 7 weeks of age, were reared in 6 rearing groups. Using a balanced design, these groups contained only horned, or only disbudded bulls (unmixed groups), or both (mixed groups), with only half of the bulls disbudded. They were slaughtered using two protocols, one with limited, the other with supplementary stress. Longissimus thoracis (LT) muscle samples were collected 48 h after slaughter and subjected to individual shotgun proteomic analysis. Results show that horn status and slaughter conditions influenced only 16 (6.2 %) and 8 (3.1 %) proteins, respectively, which is not more than expected by random error. By contrast, rearing conditions influenced 40 (15.5 %) of the identified proteins, which is significantly more than expected by random error. Eighteen of these differentially abundant proteins were involved in energy metabolism, and 9 in muscle structure and contraction. Overall, these proteins indicated greater glycolytic capacity and greater proportions of fast twitch fibres in the LT of bulls in mixed groups. These results are coherent with the lower physical activity and different physiological stress reactivity of these same mixed groups of bulls as reported in previous companion studies.