Study On The Quality Evaluation Of Starea And The Effects On Nitrogen Metabolism In Lactation Dairy Cows

Starea as slow-releasing urea feedstuff is widely concerned about the application in ruminant .We have done a systematic research on quality status of starea in China,the main production process and quality evaluation methods of starea and the effection on production performance and nitrogen metabolism in lactating dairy.Our study aims to provide the scientific basis for the establishment of quality evaluation system and the application in ruminant animals effectively and safely.Experiment 1 studied the quality of starea of different sources by collecting from the market. We collected 22 samples from 8 representative enterprise in Beijing, Hebei, Inner Mongolia and Heilongjiang.We detected the conventional index of starea such as the moisture, ash, crude protein and urea et al and gelatinization degrees and starch content;by the method of thermostatic urease in vitro,we test the slow release of urea of starea;we also detected the melamine and cyanuric acid in the products; Results indicated that,conventional index of starea from market has larger variation, the variation in turn by big to small for index is protein equivalent, urea, ash, moisture.The variation among gelatinization degrees and starch content are also larger,all of the starch content in starea is low,we proved that we could not compare the quality of stareas by gelatinization degrees until they were same in the starch.The cyanuric acid can be detected in product but not melamine.We can evaluate the quality of starea by the ureal slow-release in 30min in vitro.Experiment 2 based on the early reseach, studied the processing technology and quality evaluation methods of homemade starea.We adopts 5×4 factorial experiment design through DSE-25 twin-screw extrusion machine to make starea in different specifications,takes the urea content and extrusion temperature as the test factors, five levels of urea content is 20%,25%, 30%, 40% and 50%, four levels of extrusion temperature is 100℃, 120℃, 140℃and 160℃. We conducted a study on the effection of different urea content and extrusion temperature on slow release of urea of starea. Results indicated that,the extrusion pressure and torque have the trend of reducing with the urea content and temperature increasing. When the urea content in starea and extrusion temperature are in 20%-30% and 120℃-160℃respectively, the product will be slow-releasing better.There were no melamine in starea,but cyanuric acid was incresed by the urea content,and the cyanuric acid also may be produced with the temperature arising.Experiment 3 studied the effection of starea on production performance and nitrogen metabolism in lactating dairy cows. Five mid-late lactating Holstein cows with rumen fistula were divided into five groups in a 5×5 latin square test design, cows of the five groups were fed with control diet without urea,U-16% diet with replacing sixteen percent of the total nitrogen of control diet with non protein nitrogen from urea,S-16%,S-24%and S-32% diet with replacing 16%,24%and 32% of the total nitrogen of control diet with non protein nitrogen from starea. The adaptive phase of the first phase is 14d and the other phase is 7d, the sampling period in every phase is 5d,all of the experiment lasted 67d.We aimed to study the effection of starea on production performance ,ammonia in rumen liquor and blood,blood urea nitrogen and nitrogen emission in lactating dairy cows. Results indicated that, replacing 16% and24% of the total nitrogen of control diet with non protein nitrogen from starea can not affect the production performance significantly(P>0.05) ,but the S-32%group has reduced the dry matter intake and milk production(P<0.05).Compared with urea,the starea can relieve ammonia concentration in rumen liquor and reduce the peak of blood ammonia concentration effectovely,but with the increasing of the starea,the peak concentration of rumen ammonia and blood ammonia were also incresed,and the the ammonia concentration of S-32% group among different cows in the same time were not stable because of the palatability. There were no significant differences(P>0.05) in nitrogen emisssion between starea and urea,which replaced 16% of the total nitrogen,but when the starea nitrogen repleased 24% and 32% of the total nitrogen,the total nitrogen excretion of nitrogen intake was increased significantly than other groups(P<0.05), it can reduce the nitrogen utilization of the diet and increase the pollution of nitrogen in environment.The starea can not cause melamine and cyanuric acid residual in milk.