Effect of some factors on relationships between milk urea levels and cow fertility
Abstract. The effect of some factors on relationships between milk urea levels and fertility of 19 028 cows was analysed. The generalized linear model (GLM) of the SAS package (SAS 2004) was used in the statistical calculations. The increase in milk urea concentration was found to increase calving interval (r=0.05, P≤0.01), rest period (r=0.07, P≤0.01), service period (r=0.01, P≤0.01) and the number of services per conception (r=0.02, P≤0.01). Therefore, dairy breeders may find it advantageous to monitor urea concentrations, which could help to improve cow fertility. Herd milk production level, age of cow and lactation period were the factors that had the greatest effect on the relationship between milk urea levels and cow fertility parameters. The relationship between milk urea level and fertility was stronger in cows from herds with >6 000 kg milk yield, in first-calf heifers and in cows at 3 months of lactation.