The genetic basis of gestation length in Bonsmara cattle

[摘要] English: The purpose of this study was to investigate the genetic and phenotypicparameters for gestation length and birth weight in Bonsmara cattle in SouthAfrica. The genetic and phenotypic parameters were determined when the traitswere firstly treated as traits of the calf and secondly as traits of the dam.A total of 26962 gestation length and birth weight records were used for thisinvestigation. The data was collected from 1989 to 2000. The phenotypiccorrelation between gestation length and birth weight was moderate and positive(0.22). The sources of non - genetic variation for gestation length and birthweight were sex, herd x year x season (HYS) and age of dam (linear andquadratic). When the traits were treated as traits of the calf all the sources ofnon-genetic variance were highly significant (P<0.001). Age of dam quadraticwas not significant for birth weight when the trait was treated as a trait of thedam.The traits were analysed through univariate and bivariate analyses. Five basicmodels were used for the univariate analysis. The five models took the directgenetic, maternal genetic, and/or permanent maternal environmental geneticeffects into account. The appropriate random effects were also included in, orexcluded from the models. The model that fitted the data best was then used fora bivariate analysis. The direct heritability through the bivariate analysis was 0.38for gestation length and 0.23 for birth weight. Maternal heritability was lower, 0.09for gestation length and 0.11 for birth weight. The direct genetic correlation (0.40)and the maternal genetic correlation (0.57) between gestation length and birthweight were positive. In the above results the traits were treated as traits of thecalf. The direct heritabilities for gestation length and birth weight, when the traitswere treated as traits of the dam, were 0.15 and 0.16 respectively throughbivariate analysis. The maternal heritabilities for gestation length and birth weightwere very low to negligible (0.02 and 0.003). The direct genetic correlation (0.41)between gestation length and birth weight was positive, but the maternal geneticcorrelation (-0.83) was negative.Estimated breeding values (EBVs) for gestation length and birth weight werecalculated for each animal in the data. The genetic trends for gestation lengthand birth weight were also determined. The trend for gestation length showedthat there was a correlated response for shorter gestation length through thepossible direct selection for lower birth weight. The trend for birth weight showedthat there was selection for lower birth weight.

[发布机构] University of the Free State