A model calculation on the prospects of an improvement of claw health in dairy cattle via genetic selection

Involuntary cullings due to feet and leg disorders are of increasing concern and reach nearly the same magnitude as those caused by fertility problems or mastitis. Conventionally, breeding programs only indirectly include a selection for improved claw health when using estimated breeding values from four different conformation traits. The direct selection path against the disorder, i.e. laminitis, seems to be more powerful to substantially improve the health status of the population. The aim of the present study was to quantify the relative importance of different index traits with respect to the selection response for the trait laminitis resistance. Index sources for estimated breeding values of bulls were laminitis observations and linear scores for hock quality of daughters and one claw measure (hardness of the dorsal wall) of the bull combined in different scenarios. The application of a selection index requires the availability of appropriate genetic parameters. The heritability estimate using logistic models for laminitis was 0.14. Genetic correlations between laminitis and conformation traits of feet and legs were, apart from those for heel depth, favourable with respect to the breeding objective. Phenotypic and genetic correlations between laminitis and claw measures of young bulls and between conformation traits scored for daughters and claw measures were near zero. Solely the claw hardness measure of young bulls seemed to be an appropriate indicator for the incidence of laminitis of daughters. Selection response in laminitis resistance per generation and accuracy of estimated breeding values of bulls could be doubled when laminitis observations of 50 daughters were included as index traits. To be effective in selection, breeding designs enabling the routine recording of claw disorders should be developed. The necessity of scoring conformation traits describing the feet and legs and the measurements of claws of young bulls is questionable with respect to the improvement of laminitis resistance and should carefully be evaluated.

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