Abstract:

The aim of this study was to evaluate the effect of starea nitrogen on production performance, ammonia nitrogen (N) concentration in rumen liquor and blood, blood urea N, and melamine and cyanuric acid residual in milk of lactating dairy cows. Five midlate lactating Holstein cows with rumen fistula were divided into five groups in a 5×5 Latin square design. The cows of the five groups were fed with control diet without urea, U16% diet with 16% of the total N of control diet replaced by urea N, and S16%, S24% and S32% diet with 16%, 24% and 32% of the total N of control diet replaced by starea N. The adaption period of the first phase was 14 d and the other phase was 7 d, respectively. The sampling period in every phase was 5 d. All of the experiment lasted for 67 d. The results showed that replacing 16% or 24% of the N in control diet with non protein nitrogen from starea did not affect the lactation performance significantly (P>0.05), but in the S32% group the lactation cows had a reduced dry matter intake and milk production(P<0.05). Compared with urea, the starea could relieve ammonia concentration in rumen liquor and reduce the peak of blood ammonia concentration effectively, but the peak concentration of rumen ammonia and blood ammonia were also increased with the increasing of the starea. The starea could not cause melamine and cyanuric acid residual in milk. It is concluded that for the dairy cows safety the proper proportion of replacing the total nitrogen of diets with starea nitrogen is less than 24%.