Application of Milk Urea Nitrigen Index (MUN I) for Monitoring Protein Nutrition Status in lactating Dairy Cow

Five herds of Holstein breed of cow were used to evaluate protein nutrition condition based upon measuring milk urea nitrogen (MUN) concentration. Five dairy cows were selected at early lactation, multiparous with days in milk 45±7 from each herd randomly. Feed and milk samples were taken over a period of 6 month between July and December 2006. Samples were collected monthly from individual cows as well as milk bulk. Diet alterations and management practices were recorded over the period of the study. The results of the present research indicated that applied diets in the herds provided the nutrients requirements of cows based on the National Research Council (NRC, 2001) recommendations. The results obtained from the analysis of variance of at milk bulk samples (with repeated measurements) showed that no any statistically significant differences were found among different herds for MUN. However, there was a significant difference of MUN among herds over the times (months) (P<0.05). Milk compositions (percentage of total solid, fat, total protein, NPN and lactose) were found to be not affected significantly by herds and month of recording. The results of analysis of variance of MUN at individual cows revealed that there were significant (P<0.05) differences among different herds and months of recording. There was a positive significant (P<0.05) correlation between MUN of milk bulk and MUN at individual cows. Month of recording had a significant influence on MUN at both levels of tank and individual cows (R2=0.75). According to the results of the present research, it can be concluded that measuring MUN at milk bulk samples could be used as an indicator of protein nutrition at herd level.