Genetic analysis of clinical mastitis data for Holstein cattle in the Czech Republic

Cases of mastitis were recorded from 22 812 lactations of 10 294 cows on seven farms in the Czech Republic from 2000 to 2012. The per cow number of clinical mastitis (CM) cases per lactation (CM1), number of days of CM per lactation (CM2), and CM considered as an all-or-none trait (CM3) with values of 0 (no CM case) or 1 (at least 1 CM case) were analyzed with linear animal models. Bivariate linear animal models were used for estimation of genetic correlations between CM traits and average lactation somatic cell score (SCS305), average 305-day milk (MY305), fat (FY305) and protein (PY305) yield, and interval between calving and first insemination (INT) and days open (DO). Factors included in the model of choice were parity, herd effect, year of calving, calving season, permanent environmental effect of the cow, and additive genetic effect of the cow. Estimated heritabilities for CM traits were in the range of 0.09 to 0.10. Genetic correlations of SCS305 with CM traits 1, 2, and 3 were 0.22 ± 0.062, 0.23 ± 0.064, and 0.29 ± 0.086, respectively; those of MY305 with the three CM traits were 0.80 ± 0.037, 0.79 ± 0.040, and 0.83 ± 0.038, respectively; those of INT with the three CM traits were 0.19 ± 0.087, 0.17 ± 0.089, and 0.26 ± 0.091, respectively; and those of DO with the three CM traits were 0.28 ± 0.089, 0.22 ± 0.091, and 0.27 ± 0.091, respectively. Knowledge of genetic parameters of mastitis incidence and assessment of the economic importance of the disease is necessary to design breeding programs to improve udder health