INDICATIONS AND IMPLICATIONS FOR TESTING OF MILK UREA IN DAIRY-CATTLE- A QUANTITATIVE REVIEW - PART 1 - DIETARY-PROTEIN SOURCES AND METABOLISM

Milk urea concentrations in dairy cattle. There has been increased use of milk urea concentration as an indicator of dietary protein intake and protein metabolism in dairy cattle over recent years. The value of milk urea content data in predicting dietary composition, particularl y for pasture-fed cattle, has not been well described. Protein metabol ism and urea synthesis. Many factors influence the degradation of diet ary proteins in the rumen, post-ruminal protein metabolism and urea sy nthesis in cattle. Strong positive correlations between nitrogenous fe rtiliser use and the crude protein content of pastures were identified by use of meta-analysis. Similar strong positive correlations were no ted between dietary protein intake, rumen ammonia and plasma urea conc entrations. The costs of urea synthesis include energy losses, and imp ortantly, the loss of endogenous amino acids, which are deaminated in the synthesis of urea. Milk urea as an indictor of protein metabolism. Urea concentrations in blood, plasma and milk are strongly correlated . Milk is an adequate indicator of blood and plasma urea content, but non-nutritional factors may significantly influence milk urea concentr ations. Recommendations for dietary protein management based on milk u rea concentrations must be undertaken with care.