Adjustments for heterogeneous herd-year variances in a random regression model for genetic evaluations of Polish Black-and-White cattle
- 68 Downloads
The study investigated the existence of heterogeneous variance in first-lactation daily milk yield of Polish Black-and-White cows across herds in different years. Bayesian Information Criterion was used to show that the model with unequal residual variances for different herd-years was more plausible than the model assuming equal variances. A method of adjusting phenotypic records was developed to account for unequal variability in herd-years. Factors used for the data adjustment considered variation of general residuals and residuals for specific herd-years. The size of herd-year was also taken into account. Varied power of corrections was used to analyze the effect of adjustment on estimated breeding values. The method was applied to daily milk records of 817 165 primiparous cows. The effectiveness of the data adjustment was evaluated by the analysis of differences between each bull’s breeding value and its parental index. Data correction reduced the average difference and variance of differences between breeding values and parental indices. Accounting for the size of herd-year classes in correction factors improved the efficiency of heterogeneous variance adjustment.
Key wordsbreeding value dairy cattle heterogeneous variance
Unable to display preview. Download preview PDF.
- Interbull 2005.www-interbull.slu.se Google Scholar
- Jagusiak W, Żarnecki A, 2002. Characteristics of bull-dam herds. Electronic Journal of Polish Agricultural Universities, Anim Husbandry 5.www.ejpau.media.pl/series/volume5/issue1/animal/art-07.html Google Scholar
- NRS, 2005. Breeding value evaluation production traits, technical information on the breeding values evaluation of the production traits. www.nrs.nlGoogle Scholar
- SAS Institute, 1998. User’s guide: Statistics, Version 7. SAS Institute, Inc., Cary, NC.Google Scholar
- Strabel T, Jamrozik J, 2006. Genetic parameters for milk production traits of Polish Black-and-White cattle estimated with large-scale multiple lactation random regression test-day models. J Dairy Sci (Accepted).Google Scholar
- Szydłowski M, Szwaczkowski T, 1993. The effect of grouping herds according to production level on the heritability of milk traits in cattle. Anim Sci Pap Rep 11: 295–300.Google Scholar