Ludmila Zavadilová, Miloslava Štípková, Alena Svitáková, Zuzana Krupová and Eva Kašná
Cases of mastitis (CM) from 38,236 lactations belonging to 16,497 cows were recorded on seven farms in the Czech Republic from 1996 to 2014. Clinical mastitis was analyzed with linear animal model as an all-or-none trait for each recorded lactation (CM305) and separately for each trimester of lactation (CM1, CM2, and CM3). Bivariate linear animal models were used to estimate the genetic correlation between these CM traits and lactation means for somatic cell score (SCS305), the interval between calving and first insemination (INT) and days open (DO). Factors included in the linear model were parity, herd, year of calving, calving season, fixed linear and quadratic regression on age at first calving, fixed linear and quadratic regression on milk production in the corresponding parity, permanent environmental effect of the cow, and additive genetic effect of the cow. Estimated heritabilities of the CM traits ranged from 0.01 to 0.03. Permanent environmental effects accounted for approximately two-thirds of the phenotypic variance. Genetic correlations of SCS305 with CM traits were 0.85±0.029, 0.81±0.086, 0.82±0.087, and 0.67±0.088 for CM305, CM1, CM2, and CM3, respectively. Genetic correlations of INT with CM305, CM1, CM2, and CM3, respectively, were 0.22±0.065, 0.19±0.084, 0.20±0.121 and 0.15±0.121: and genetic correlations of DO and the four CM traits were 0.28±0.079, 0.26±0.101, 0.43±0.134, and 0.15±0.131. For the 140 sires in the dataset, Spearman rank correlations among breeding values for the four CM traits and for SCS305 were uniformly high at 0.99±0.001.
Zuzana Krupová, Ludmila Zavadilová, Marie Wolfová, Emil Krupa, Eva Kašná and Petr Fleischer
The aim of the study was to investigate the impact of the implementation of new health traits into the breeding objective and selection criteria for Czech Holstein cows on the genetic selection response in the breeding objective traits. Incidence of overall claw diseases was included into the current breeding objective for cows (11 traits together). Three traits that indicated claw health (incidence of claw diseases overall and infectious and non-infectious claw diseases) and incidence of clinical mastitis were successively added to the current selection criteria in a cow selection index (a maximum of 19 traits). Selection responses in the breeding objective traits were estimated by applying the general principles of the selection index theory. The required genetic variances for the new traits, the economic weights for all breeding objective traits and the genetic correlations among the selection index traits were estimated within this study. The marginal economic weights, which were calculated for two-year-old cows by applying a bioeconomic model with implemented gene flow, were -193 and -168 € per case for clinical mastitis and overall claw disease incidence, respectively. Using the comprehensive selection index with 19 traits, the reduction in the incidence of both udder and claw diseases was calculated to be 0.004 cases per cow per year. At the same time, a more favourable genetic selection response was obtained for other functional traits, e.g., +0.020% for cow conception rate and +0.010 years for productive life of cow (which represented the profit of 67 € and 367 € per herd and per year, respectively) when compared to the current index. Based on this study, a direct selection of cows for claw and udder health is nowadays recommended to improve the health status of herds and economics in production systems.