Abstract
Effects of composite β–κ-casein genotypes and β-lactoglobulin genotypes on age at first insemination and length of service period of 17,059 Finnish Ayrshire heifers, and on days from calving to first insemination and length of service period of 17,869 first lactation cows were estimated. A mixed linear model under an animal model was assumed. The effect of the β–κ-casein genotypes on days from calving to first insemination (DFI) was statistically significant. The difference in DFI between the rare extreme β–κ-casein genotypes A 1A 2BB and A 1A 2EE was about 19 days (0.75 phenotypic standard deviation), but the standard errors of the effects of these genotypes were large. Between the most frequent β–κ-casein genotypes the differences in DFI were negligible. The other reproduction traits studied were not affected by composite β–κ-casein genotypes or β-lactoglobulin genotypes. Based on the results presented in this study, selection based on β–κ-casein and β-lactoglobulin polymorphism should thus have no substantial impact on fertility of Finnish Ayrshire heifers and cows.
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