Utilization of Milk Urea Concentration to Study Nitrogen Use Efficiency in Haouz Dairy Herds of Central Morocco

Abstract

This study was conducted on ten commercial dairy herds, over one year to explore effects of feeding strategies on milk urea concentrations as a predictor of efficiency of nitrogen (N) utilization and urinary nitrogen excretion in dairy cows. Milk samples were collected monthly and analyzed for milk urea concentrations using a colorimetric procedure. Feed samples were characterized and their concentrations of protein digestible in the intestine and net energy for lactation were calculated according to the French system of PDI. Regression equations were performed to predict nitrogen in milk and urinary nitrogen excreting. Averages values were 28.3±2.1 mg.dl^-1 for milk urea concentration, 26.8±5.1% for efficiency of N utilization and 178±16.2g/d for urinary nitrogen excreting. Significant correlation between urea in milk and crude protein content, milk production and urinary nitrogen excretion was observed (P<0.01). Negative association was found between efficiency of nitrogen utilization, milk urea content, urinary nitrogen excreting and milk production yield.