The Association between milk urea nitrogen and production variables in Iranian holstein dairy herds

A study was conducted to collet data from dairy herd monthly tests with 12218 records، to investigate the association between milk urea nitrogen (MUN) concentration and milk yield، milk protein، milk fat percentage، SCC، and parity for three commercial Holstein herds in Tehran. Mean MUN، categorized by 30-d increments of days in milk (DIM)، paralleled changes in milk values and followed a curvilinear shape. Mean MUN for Holstein cows was 19. 78 mg/dl. For cows، concentrations of MUN were different among lactation groups 1، 2، and 3+ (p<0. 01). In order that، MUN concentration decreased with progression of parity. The relationship between MUN and milk yield was positive so that the highest concentration of MUN was related to the cows with the highest milk yield. In Overall، concentrations of MUN were lower during for the first 30 DIM compared with all other DIM categories for cows. Milk fat and milk protein percentage were significantly different between the levels of milk urea nitrogen concentration. Fat to protein ratio was also significant among the levels of milk urea nitrogen concentration for cows. As the milk protein percentage increased، MUN concentration decreased، Milk fat percentage also decreased as MUN increased. There was a negative relationship between Somatic cell count and MUN concentration. This study found that MUN can be used as profitable tool in herd management and determining nutritional status of dairy herds.