Genetic group and heterosis in the behavioural evolution of steers during finishing in confinement

Abstract

Crossbreeding is one way of achieving complementarity between breeds in relation to economically important characteristics; in addition, it allows the effect of heterosis to be exploited. The aim of this study was to measure the behavioural evolution of different genetic groups and mating systems in continuous alternating crosses of Charolais and Nellore cattle. Seventy-nine purebred Charolais (C) and Nellore (N) steers were evaluated during finishing in confinement, together with their second (3/4C 1/4 N and 3/4 N 1/4C), third (5/8C 3/8 N and 5/8 N 3/8C) and fourth generation (11/16C 5/16 N and 11/16 N 5/16C) crosses. The confinement period was 97 days, including 13 days for adaptation to the environment and feeding regime. Behavioural assessments were carried out when weighing, evaluating the composite scale score, time taken to exit the scales, measurement of flight distance, location of the facial hair whorl, and plasma cortisol level at slaughter. The Charolais animals showed a better composite scale score, longer exit time and shorter flight distance than the Nellore animals. For generation 3 (5/8 animals), the inclusion of Charolais genes afforded a higher composite scale score in each of the assessments, longer flight time in the assessments at 14 and 77 days, shorter flight distance in each of the assessments, with the facial hair whorl positioned further below the eye line, determining animals of a calmer behaviour. Purebred Nellore and predominantly Nellore animals from the third generation of crosses were higher in cortisol at slaughter than the purebred Charolais or predominantly Charolais animals, showing significant heterosis only in the second generation. Bos taurus animals are calmer and have a more suitable temperament than Bos indicus, however, the behaviour of zebu cattle can improve as the period of confinement increases, with the type of handling affecting behaviour and reactivity throughout the assessments.