Association between milk breeding values and phenotypic conformation traits in pure‐dairy and dual‐purpose cows

Abstract

IntroductionMany studies (N orman et al. 1988; M eyer et al. 1987; H arris et al. 1992; M iztal et al. 1992) have examined the relationship between conformation and yield traits in term of genetic correlation. Traits describing the shape of the udder are highly to moderately correlated with milk yield. However, results obtained with correlation analyses do not account properly for the ordinal nature of conformation traits. With the exception of stature, conformation scores are usually subjective, non‐numeric qualitative variables and an increase from score 1–2 does not necessarily correspond to an increase from score 7–8. Theoretically, every score should be compared with another only in terms of a ‘greater than’ or ‘less than’ relationship. Correlation expresses the strength of the linear relationship between milk and type traits, assuming that differences between two adjacent points on any part of the scale are equal.In Belgium, dairy breeds are exploited mainly for two purposes, either for milk production only (mainly Holstein cows) or for milk and meat production (mainly Red and White, West Flemish Red, East Flemish Red Pied and Meuse Rhine Ysel). The authors are unaware of any description of the relationship between yield traits and conformation traits for those breeds in Belgium. If several conformation phenotypes are identified as important predictors of milk estimated breeding values, if they are measured early in life before milk estimated breeding values are computed, and if these predictors have no known negative side‐effects on cows’ profitability, then those conformation traits could be used for mating decision‐making. Indeed, dairy producers are usually able to evaluate their cows’ conformation. This information could then be used before milk estimated breeding values are available, or when they are not available, as is the case for non‐registered cows. In the Southern part of the country, only 25% of all cows are registered (D etilleux et al. 1997).The objectives of this study were (1) to determine whether phenotypic values for conformation traits are related to milk breeding values in pure‐dairy and dual‐purpose breeds; (2) if so, to find type scores predicting best high breeding values for milk; and (3) to validate type scores obtained in (2).