ABSTRACT
Bovine respiratory diseases (BRDs) have major socioeconomic impacts in the beef sector. Antimicrobials have been traditionally used to prevent the development of BRDs upon arrival in fattening units. Currently, from a "One Health and One Welfare" perspective, alternative solutions are being investigated. Preconditioning programmes that aim at reducing stress and reinforcing immune functions have been proposed to decrease BRDs incidence. In this study, we assessed the effect of a preconditioning protocol set up in nine commercial beef herds on young bulls' behaviour, health, and performance. Preconditioned bulls (PREC) were weaned indoors 50 days before departure, and progressively fed a concentrate diet supplemented with vitamins and trace elements. They also received an anthelmintic treatment, and two doses of a trivalent vaccine against respiratory pathogens at 4-week intervals. In contrast, controls (CTRL) were kept on pasture with their dams with no vaccination or particular diets. All calves were transported together to a single sorting facility to be sorted by experimental groups, origins, and BW, forming new groups before dispatch to four fattening units. At arrival, CTRL were treated with anthelmintic drugs and received one injection of the same BRDs vaccine. No intervention was performed on PREC bulls. BRD-scores were 0.73 in PREC versus 0.07 in CTRL (P = 0.01) during the preconditioning period and 0.96 in PREC versus 0.54 in CTRL (P = 0.41) after 15 days in the fattening units. Morbidity estimates were 18% in PREC versus 1% in CTRL (P < 0.001) during the preconditioning period and 32% in PREC versus 19% (P = 0.07) in CTRL after 15 days in the fattening units. Poor housing conditions during preconditioning and a different aetiology could partly explain these results. At arrival to fattening, the average daily gain (ADG) was 1 605 g for PREC versus 1 140 g (P = 0.012) for CTRL. After fattening for 180 days, differences in BW, ADG, carcass weight and conformation were inconclusive. In Europe, preconditioning programmes including vaccination must be set up coherently with good husbandry practices and with a global adaptation of batch management of the beef sector otherwise, they may be less effective than expected.