Genetic studies of beef characteristics in Swedish cattle breeds

This thesis, comprising four papers, considers various aspects of genetic evaluation for beef production. The main objectives of the studies were: to assess the possibilities of using ultrasonic scanning measures, muscularity scores and body measures recorded on young dairy breed bulls as selection criteria for beef production ability; to investigate genetic and phenotypic variability in growth traits of male and female calves and estimating genetic trends for growth traits in Swedish beef cattle breeds. It was shown that scanning measurements, body measures and muscularity scores are heritable traits. The predictive value of these on carcass traits was demonstrated in Friesian cattle, indicating an influence on carcass conformation and dressing percentage. Differences were revealed between beef breeds as well as between sexes within breeds in estimated heritability for weaning gain (WG), maternal WG and postweaning gain (PWG) in calves. Genetic correlations between growth rate observed in male calves and in females on average 0.6-0.7 for both WG and PWG. Positive genetic correlations and negative residual correlations were disclosed between WG and PWG. In an example with Hereford the genetic trend was seriously underestimated when the traits were not analysed together. Estimated genetic trends for WG and PWG were positive in all breeds (Hereford, Charolais and Simmental), although, low selection differentials in both sires and dams were revealed for both traits. In general, the studies indicate the potential of the multiple trait animal model approach, where all avialable information on relatives and correlated traits is utilized in the analyses. The thesis discusses various aspects influencing selection for beef-production ability, such as selection criteria, variation in estimated genetic parameters between breeds and sexes, and alternative beef production strategies for dairy breeds. Furthermore, the prospect of a Total Merit Index in beef cattle is described, combining growth and carcass traits with calving performance.