Milk Urea Nitrogen and Fertility in Dairy Farms

To evaluate the association between Milk Urea Nitrogen (MUN) and fertility of early lactation dairy cows, reproductive and productive data and MUN measurements from 10 dairy herds in northeast of Iran between 2005 and 2008 were analyzed by survival analysis and the Cox proportional hazards model. Days from calving to conception or to the end of the study were used as the outcome. The mean MUN values in the first 3 months of lactation were used to reflect the MUN status of a cow. Parity, mean milk yield, mean milk fat percentage and herd were included in the models as fixed effects. Cows with WIN values of 12-13.99 and 14-15.99 mg dL(-1) had higher fertility (15 and 8%, respectively) and cows with MUN value above 18 mg dL(-1) had lower fertility (10%) than cows with MUN value below 12 mg dL(-1) (p<0.0001). The results indicate that increasing MUN levels above 18 mg dL(-1) appears to be negatively related to dairy cow fertility only in first parity (p<0.01). It is also suggested that the levels of MUN that are adversely associated with fertility, might be <12 and >18 mg dL(-1).