Investigation of milk urea nitrogen concentration and factors affecting its variation in Greek Holstein herds

Abstract

Milk urea nitrogen (MUN) is an important tool in dairy cow nutrition, as it reflects the amount of nitrogen in the diet which is not used for production. The objective of this study was to evaluate MUN values in Greek dairy herds, for the first time, and to investigate the source of its possible variation. For this purpose, a dataset of 23,266 milk records from 24 Holstein herds in the region of Thessaly (Greece) was used. Descriptive statistics, analysis of variance and a multiple regression model were used for statistical analysis. Significant differences were observed among farms (P<0.05). Mean MUN concentration was 15.54 mg/dL. More than 90% of the measurements were above the upper limit of reference herd target-values. In contrast with previous observations, lower MUN values (P<0.05) were observed during the summer and autumn. A positive relationship between milk yield and MUN was observed, but only up to MUN values of 16 mg/dL. Milk fat content and fat/protein ratio were negatively related to MUN, while cows with higher protein content had lower MUN values (P<0.05). Most milk traits and sampling month explained only 25.8% of the variation in MUN concentration (P<0.05). In conclusion, MUN values in Greek dairy farms were greater than target-values suggested for most herds, indicating systematic nutritional errors that could affect health and reproductive performance of dairy cows.