Relationships between predicted transmitting ability of Gyr bulls and the milk production of their straightbred Gyr and crossbred progenies

[摘要] - Milk production records of 5,258 lactations at first calving from straightbred Gyr and crossbred Gyr:Holstein cows were used to evaluate the relationship between sire predicted transmitting ability (PTA) and the milk production of their progeny. Animal model was used to calculate the PTA using straightbred Gyr daughter only, the crossbred Gyr daughters only and all daughters at the same time. Subsequently, the PTA regressions and correlations of the sires obtained under different alternatives, with the straightbred and, or crossbred daughters production were estimated. The estimated regression coefficient of PTA of 48 Gyr bulls evaluated with straightbred Gyr daughter production on their crossbred daughters milk production was 0.75, while the regression coefficient of PTA of 50 Gyr bulls evaluated on crossbred daughter production on their straightbred daughters production was 1.11. The correlation coefficients between PTA of the sires and daughters milk production for the different alternatives ranged from 0.05 to 0.17. The rank correlation among PTA ranged from 0.34 to 0.94, were the smallest observed between PTA on crossbred daughters and PTA on straightbred Gyr daughters, and the highest, between the PTA observed by the weighed PTA means from straightbred and crossbred daughters with PTA observed with data from straightbred daughters.

[学科分类] 兽医学

[关键词] correlation;genetic evaluation;Gyr cattle;milk production;PTA;regression     IntroduçãoO melhoramento genético de bovinos de leite tem-se baseado;ao longo dos anos;na seleção de indivíduos que apresentam um diferencial melhorador de genética aditiva em relação aos seus pares