Genetic parameters for scrotal circumference and weight traits in Black Hereford cattle

The scrotal circumference of yearling bulls and its relation to productive and reproductive traits has been previously studied in major commercial beef breeds. This study evaluates the heritability of yearling scrotal circumference and its relation to weight traits in Black Hereford cattle. Records for yearling scrotal circumference (YSC; n = 894), birth weight (BW; n = 2350), weaning weight (WW; n = 2077) and yearling weight (YW; n = 1434) were obtained in Black Hereford cattle. Genetic parameters were estimated using an animal model. The final model for YSC included the age at measurement as covariate and fixed effects of birth year, the observer and the age of dam. The final models for BW, WW and YW included the age at measurement (if available) as covariate and fixed effects of birth year, age of dam, sex and embryo transfer. Random effects in the four models were additive genetic effects. The four-trait animal model was fitted by best linear unbiased prediction with restricted maximum likelihood (co)variance estimates. A univariate model for yearling scrotal circumference was also estimated by a Markov chain Monte Carlo algorithm. Heritabilities were estimated at 0.49, 0.43, 0.47 and 0.45 for YSC, BW, WW and YW, respectively. These estimates are moderate to high and indicate that selection for these traits is possible in Black Herefords. Genetic correlations of 0.22, 0.54 and 0.59 were found between YSC and BW, WW and YW, respectively. The genetic correlation between WW and YW was estimated at 0.89. The relation of YSC to the age at first calving in the bulls daughters could not be studied due to less consistent data of the age at first calving. An increase of YSC and weight traits was found in bulls of older dams. Expected progeny differences for YSC, BW, WW and YW were proposed for 4099 Black Herefords. These expected progeny differences can be included in a breeding program.Master's dissertationstatus: publishe