Heterose nos indicadores fisiológicos e comportamentais de bovinos de corte

Abstract

The use of crossbreeding can be a good tool for complementarity between breeds, taking advantage of the heterosis effect. The crossing between zebu and taurine breeds stands out over other mating systems, due to the existing genetic distance. In view of this, the objective of this work is to measure the degree of heterosis in behavioral and physiological traits in different genetic groups resulting from the crossing of animals of the Charolais and Nellore breeds. Cattle kept in confinement were evaluated, represented by 79 castrated males divided according to eight degrees of Charolais x Nellore blood. The total period of confinement was 97 days, with the first 14 days of adaptation to the environment and feed regimen. The animals were weighed at the beginning and end of the experimental period, as well as every 21 days, after a 14-hour fast. The traits evaluated were: compound score (Piovesan, 1998), flight time (BURROW & DILLON, 1997), flight distance (BOIVIN et al., 1992), location of facial hair, and level of plasmatic cortisol. The inclusion of Charolais genes provided an increase in the time of leaving the balance in the steers, making positive values of the characteristic in relation to the Nelore and a decrease with the inclusion of the Nelore gene, with negative values of variation of the composite score of the balance. For the characteristic flight distance, only pure Charolais animals showed values lower than 35 days of confinement. However, at 55 and 76 days of confinement, in addition to purebred Charolais, animals with the highest degree of Charolais blood in generation three also showed lower values. On the other hand, higher values for the trait were identified in pure Nelore animals and with Nellore predominance in generation three, at 55 and 76 days of confinement. Purebred Nellore animals and those with Nellore predominance showed higher values for the swirl trait, compared to pure Charolais animals or animals with a higher degree of Charolais blood. When compared between the different mating systems, the trait did not differ (p>0.05) among animals from generations two, three and four, however, it differed from purebred animals, which had a lower average. With regard to physiological indicators, purebred Charolais animals had a higher cortisol value (Table 6) when compared to purebred Nellore animals. On the other hand, a higher value for cortisol was reported in animals with a greater increase in Nellore blood, in the third generation. Cortisol did not differ (p>0.05) between mating systems. In relation to the purebred animals, it was verified that the Charolais animals are calmer, having better values in all the traits. When there is difference in evaluations, within generations, animals with predominance of Nellore blood are more reactive. Management also influences behavior and reactivity throughout the evaluations.