Correlations between Milk Urea or Plasma Metabolites and Milk Fat and Protein Concentrations in Dairy Cows

Abstract

Ninety pair samples of morning and evening milk and blood plasma were collected from 7 dairy cows fed on various feeding systems after 4 weeks postpartum, and milk urea N (MUN) and blood metabolite levels as well as fat and protein concentrations in milk were determined. MUN levels were correlated with those of blood urea N (BUN). In milk samples with significantly lower or higher MUN, protein levels were lower. The milk protein levels were lower also in cases with lower plasma glucose levels. The declined levels of milk protein seemed to reflect eitherinsufficient intake of dietary protein (or nitrogen) or deficiency of available energy from the diets. Milk fat levels were not significantly correlated with MUN or plasma metabolite levels.