The effect of milk urea level on fertility parameters in Holstein–Friesian dairy cows

Abstract

The objective of this study was to reveal the effect of milk urea levels on the fertility of dairy cows, taking into account theirage, herd production level, number of cows, season of first insemination, which were analyzed using data from the SYMLEK nationalsystem. The study included data on milk urea levels in 88,745 test-day yields of 55,685 Holstein–Friesian cows, which were milked upto 30 days before first insemination, during the period preceding 180 days of first and second lactation. The GLM procedure of the SASpackage was used in the statistical calculations. Considering the observed significant relationships and tendencies, a milk urea levelhigher than 300 mg/L was found to negatively affect reproductive efficiency in dairy cows, although the effects of the urea level could bemasked by the more profound impact of environmental factors. Regardless of the factors, an increased milk urea level was paralleled bydecreased cow fertility, with statistically significant differences occurring only for the interactions with herd production level and withherd size. The unfavorable effect of the increase in the level of urea in milk (from ≤150 to >300 mg/L) on cow fertility was particularlyevident in the highest producing herds (>9000 kg milk).