Genetic correlations among longevity, claw and leg health evaluated in the nordic countries and type traits evaluated in USA, in Holstein Dairy Cattle

Sammanfattning: The Holstein breed is known for its high milk yield and this has been achieved partially by genetic selection for yield. As a consequence, functional traits have deteriorated. Claw and leg disorders are common reasons for involuntary culling: 8.4% to 8.9% of the Swedish Holstein dairy cattle were culled because of claw and leg problems during 2011 to 2014 and a Swedish dairy cow is productive on average 2.5 lactations. In 2011, a claw health index was included in the selection index of the Nordic countries (Sweden, Denmark and Finland), the Nordic Total Merit index (NTM), to improve claw and leg health and thereby also longevity. Since bulls from USA lack the information about claw disorders, would it be possible to use type traits as indirect traits for improving claw and leg health traits through breeding? The aim of this study was to investigate if type traits estimated in USA could be used to select for improved claw and leg health and longevity in Holstein cattle in the Nordic countries. Genetic correlations have been estimated between, on one hand, estimated breeding values (EBVs) for type traits estimated in USA, with), on the other hand, EBVs for longevity, claw and leg health obtained from Nordic Cattle Genetic Evaluation (NAV). Two data files were obtained, one from Holstein Association USA Inc. and one from NAV. The data file from Holstein Association USA Inc. contained EBVs for type traits and the file from NAV contained EBVs for longevity and claw and leg health traits, for Holstein bulls with a minimum of 20 daughters. The data files were merged and that resulted in 610 bulls that had EBVs for claw and leg health – and type traits while 606 bulls had EBVs for longevity traits. Reliability values were estimated from the mean number of daughters and the heritabilities for the various type traits from USA, while reliability values for the traits obtained from NAV were included in the data. Reliability values were then used to adjust the Pearson correlation coefficients between EBVs to estimate the genetic correlations. Significant results were further tested for linear and quadratic regressions. In general, estimated genetic correlations were low and close to zero. Genetic correlations that were significantly different from zero were found between Longevity in lactation 1 – 5 (L1 – L5) and Stature (0.10 – 0.12), Sole ulcer (SU) and Strength (0.13), Claw index (CI) and Strength (0.12), SU and Body depth (BD) (0.16), CI and BD (0.16), Corkscrew claw (CSC) and Udder depth (UD) (0.13), CSC and Front teat placement (FTP) (-0.17) and CSC and Rear teat placement (RTP) (-0.13). All positive genetic correlations indicate that high scores for the type trait would increase longevity or resistance against claw disorders, while negative correlations indicate a decrease in longevity or resistance against claw disorders, if high scores are given for the type trait. Noteworthy, none of the feet and leg type traits showed genetic correlations different from zero with any of the claw and leg health traits, however, some udder type traits did. The test of linear and quadratic regressions did not show any significant results. Based on the results from this study, EBVs for type traits estimated in USA are not suitable to use as indirect traits for the improvement of claw and leg health and longevity in the Nordic countries, if the improvement should be effective. The genetic progress within claw and leg health traits could be hampered when semen from bulls, which lack EBVs for claw and leg health, is imported to the Nordic countries. Therefore, including a claw and leg health index in other countries would be preferable.