Safety Evaluation Of Urea Used In Ration Of Lactating Dairy Cows

The aim of this study was to assess the effects of urea on the production performance and relatedphysiological parameters of blood in lactating dairy cows. The milk compositions (including milkprotein, milk fat, milk lactose) and the melamine and cyanuric acid in feed and milk were determinedfor safe use of urea.Thirty healthy lactating Holstein dairy cows were randomly divided into5groups, with6heads ineach group and fed for56days. Six treatments consisted of a positive control, a negative control, and3urea treatment groups. The control group was fed basal diet with13.7%of protein. The negative groupwas fed with diet containing84%of protein of the control group. The3urea treatment groups includingthe U-16, U-24and U-32group were substituted16%,24%and32%of total nitrogen of the controlgroup for urea, respectively. The milk composition, milk urea nitrogen, blood urea nitrogen, bloodammonia and the melamine and cyanuric acid in feed were determined.The results showed that there were no adverse impacts on milk yield, milk composition andphysiological parameters of blood when16%of nitrogen was substituted by urea. However, when thereplacement ratio of nitrogen was up to24%and32%, the dry matter intake and milk yield werereduced significantly, and the concentration of blood urea nitrogen and ammonia was increasedsignificantly (P＜0.05). No melamine and cyanuric acid residues that were detected in milk. Therefore,in the study, urea nitrogen substituted16%of diet total nitrogen was relatively safe, and urea nitrogensubstituted diet total nitrogen more than24%, health and production of lactating dairy cows wasnegatively affected.