Effects of herd origin, AI stud and sire identification on genetic evaluation of Holstein Friesian bulls

Abstract

The purpose of this study was to estimate the effects of herd origin of bull, AI stud and sire identification number (ID) on official estimated breeding values (EBV) for production traits of Holstein Friesian proven bulls. The data included 1,005 Italian Holstein-Friesian bulls, sons of 76 sires, born in 100 herds and progeny tested by 10 AI studs. Bulls were required to have date of first proof between September 1992 and September 1997, to be born in a herd with at least one other bull and to have sire and dam with official EBV when bull was selected for progeny testing. Records of sires with only one son were also discarded. The dependent variable analyzed was the official genetic evaluation for a “quantity and quality of milk” index (ILQ). The linear model to predict breeding values of bulls included the fixed class effects of herd origin of bull, AI testing organization, birth year of bull, and estimated breeding values of sire and dam, both as linear covariates. The R2 of the model was 45% and a significant effect was found for genetic merit of sire (P < 0.001) and dam (P < 0.014), for herd origin of bull (P < 0.01) and for birth year of bull (P < 0.001). The effect of AI testing organization was not significant. The range of herd origin effect was 872 kg of ILQ. However, in this study, the causes of this result were not clear; it may be due to numerous factors, one of which may be preferential treatment on dams of bulls. Analyses of residuals on breeding value of proven bulls for ILQ showed a non significant effect of sire ID, after adjusting for parent average, herd origin effect and birth year effect. Although the presence of bias in genetic evaluation of dairy bulls is not evident, further research is recommended firstly to understand the reasons of the significant herd origin effect, secondly to monitor and guarantee the greatest accuracy and reliability of genetic evaluation procedures