Abstract. Title of the paper: Relations between milk yield and fertility after strong increased milk yield
The purposes of the study were to estimate genetic parameters for milk production and fertility traits. The study included data on about 75,000 first and 40,000 second parity cows of German Friesian. The estimated coefficients of heritability for milk, fat and protein yield were in comparison to other previous estimates relatively high. In contrast to that, heritability of fat and protein content was very low. As expected, heritability of fertility also was very low, ranging from 0.009 to 0.127, depending on trait. Genetic correlation between milk, fat and protein yield, and fertility traits were high and unfavourable and characterize an antagonistic relation. The estimated environmental correlation coefficients are negible. The genetic coefficients of regression between milk yield and fertility are low and vary between the pair of traits. Low genetic coefficients make the effect of antagonism less strong.