Genetic correlation between feet and leg type traits and claw health in Swedish dairy cattle

Sammanfattning: With the rapid increase in herd size over the last decade, it is imperative in modern dairy cattle farming to work for good claw health, both from an economic and animal welfare point of view. Claw health is maintained by managemental and genetical pre-cautions. Poor claw health may result in lameness (Murray et al,. 1996). Among hous-ing factors flooring is of high importance especially in loose housed animals as cows need to be able to commute comfortable between lying areas, feed troughs and milk-ing facilities to stay healthy. Claw diseases and lesions have been recorded by foot trimmers at maintenance foot trimming in Sweden since 1996 and is a potential new trait for genetic evaluations. The aim of this study was to estimate genetic correlations between claw diseases (dermatitis, heel horn erosion, sole haemorrhage and sole ulcer) recorded by claw trimmers and some feet and leg type traits (rear leg side view, rear leg rear view, hock quality, bone structure and foot angle) measured by educated classifiers. The purpose was also to estimate heritabilites and genetic correlations among type traits. The data was based on observations from Swedish Holstein (SH) and Swedish Red (SR) in their first lactation. The records were collected for the Swedish Dairy Asso-ciation by claw trimmers and type trait classifiers from year 2000 to 2007 in 144 898 SH and 142 647 SR. Of these, 99 835 SH and 104 227 SR were scored for type traits while 65 789 SH and 58 457 SR were scored by claw trimmers. The results show that the heritabilites for type traits were low to medium high for both breeds. Foot angle had the lowest heritability (0.11 for SH and 0.10 for SR) while bone structure had the highest heritability (0.23 for SH and 0.31 for SR). The genetic correlations were low for both breeds, with the lowest value of -0.001 (foot angle ver-sus bone structure) for SH and -0.02 (rear leg side view versus hock quality) for SR. The highest correlations of type traits were very high with 0.87 for SH and 0.92 for SR (bone structure versus hock quality). The correlations between type traits and claw disorders were low but in general higher for SR than SH. The highest correlations for SH were found between rear leg side view and the different claw disorders with a range between 0.13 to 0.28. For SR, the highest correlations were found between hock quality and bone structure and the different claw disorders, -0.10 to -0.31 and -0.17 to -0.24 respectively. The heritabilites and genetic parameters for type trait data were similar to other inter-national studies. Some breed differences were found for genetic correlations between type traits and claw disorders. The genetic correlations were non-significantly differ-ent from zero for most traits in SH or low for SR Thus, indirect selection for im-proved claw health using type trait data was not found possible. Accordingly, it is of highest importance to continue recording of claw health as a direct way of genetic improvement of claw health instead of the indirect selection via type traits.