Özet:

A total of 88,745 test-day milk yields (obtained up to 30 days before first insemination) from 55,685 Polish Holstein-Friesian cows were used to estimate the coefficients of simple correlation between milk urea level and selected indicators of fertility, age of cows, milk production level, herd size, season of first insemination, and lactation period. The increase in milk urea level had a significant (P  ≤  0.01) effect on prolonging the calving interval (r = 0.03) and service period (r = 0.01), as well as on increasing the number of inseminations per conception (r = 0.02). The direction and magnitude of the relationships (expressed as the coefficient of correlation) between milk urea level and fertility varied within classes of cow’s age, lactation period, season of first insemination, milk production level, and herd size. The present study showed that it would be beneficial to monitor dairy herds of Polish Holstein-Friesian cows for milk urea level which could contribute to improving their fertility.

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