Cows of different breeds with high lifetime production were analysed in order to choose the best producers for embryo donors. The cows were ranked based on their milk protein yield, and a rank correlation was calculated between milk and protein yield and age. The probability of a correlation breaker was also investigated. In the Swiss Simmental breed it was found that the lower the protein production, the lower the correlation. This tendency was characteristic for the Brown Swiss population, too. In the first Osnabrück Holstein subpopulation a close correlation (0.74) was found, but not in the other two. The ratio of correlation breakers in the three subpopulations was 12.5%, 33.3% and 56.3%. In populations of German Black & White and Red & White the correlation was very close (0.9 and 0.84, respectively). The ratio of correlation breakers was 26.7% and 22.2%. In the Hungarian Holstein population the correlation was weak (0.29), so the ratio of correlation breakers was relatively high. The value of the rank correlation coefficient between the milk fat and milk quantity of the top cows of the Jersey breed was 0.26, indicating a weak correlation. The ratio of correlation breakers was 36.4%.
Genetic analysis of fertility in the Italian Brown Swiss population using different models and trait definitions
