| With the development of animal husbandry in China,the demand for feed is increasing,and the contradiction between the shortage and demand of feed resources,especially protein feed,is becoming more and more prominent.Protein is the main limiting factor in ruminant nutrition.However,the high price of protein feed such as soybean meal is one of the main restricting factor.Ruminants have a special urea cycle that can utilize non-protein nitrogen(NPN)such as urea.Rational addition of NPN to ruminant diets can reduce the amount of feed protein,which can save the protein resources and greatly reduce the feed cost.The current experiment is to supplement slow release urea for dairy heifers,beef cattle and yak,and to provide reference for ruminant production.In experiment ?,Effects of slow-release urea inclusion on rumen fermentation characters were studied by in vitro method.Four levels of slow release urea(0,1%,1.5%,and 2%)were added to rumen fluid from dairy cattle.The results showed that inclusion of 1% slowing-release urea resulted in the highest substrate degradation rate,total gas production and TVFA after 72 h fermentation.Inclusion of 1% slowing-release urea showed lowest methane production.In experiment ?: 16 healthy Holstein dairy heifers with good body condition and body weight of 322.5 ±39.4 kg were randomly divided into 4 groups,each group with 4 cows,fed with a diet of 0,1%,1.5% and 2% of slow-release urea respectively.According to the formula recommended by NRC 2001,800 g average daily(ADG)nutritional requirement was formulated for 75 days.The results showed that the group with 2% NPN supplementation had the iron deficiency anemia symptom.However,the physiological indexes of blood routine in the 1% and1.5% supplementation groups were not significantly different compared with control group.However,their ADGs were significantly higher than control and 2% supplementation group.The results showed that the supplementation of 1% to 1.5% slow release urea in the diet did not show harmful effect on the dairy heifers,but also obtained maximum ADG.In experiment ?: This experiment is to explore the difference of blood physiological and biochemical indexes and Growth performance of crossbred beef cattle(Qinchuan ×Simmental)and yak.[Method] Eight 1-year-old beef cattle(259±33 kg)and eight 4-year-old yak steers(200±11 kg)with similar body weight were divided into 2 groups.Two levels of non protein nitrogen diet(LNPN,1.5% slow-release urea in the diet)and high non protein nitrogen diet(HNPN,1.5% slow-release urea in the diet)were fed to each group of beef cattle and yaks.This experiment consistent of a 10-d adaption period and 50-d sample collection period.[Result] The results showed that both yak and beef cattle showed the highest average daily feed intake and the minimum feed to weight conversion ratio under LNPN treatment.NPN supplementation showed non-significant influence on the blood parameters both for beef cattle and yak steers.The ration did not show different effect on the blood RBC and HGB for the two breeds.However,the blood MCV,MCHC,MCH and RDW of yak steers were significantly higher than beef cattle.Different NPN levels did not significantly affect the serum biochemical parameters of beef cattle and yaks.The serum TP,UN,IgA,IgG,IgM of yak were higher than that of beef cattle.The serum ALB levels of yak under HNPN treatment were significantly lower than those under LNPN treatment.The results indicate that it is feasible to add 1% of slow-release urea in the diet of beef cattle and yak.And allopatry fattening low altitude showed unharmful effect on the health of yak.The experimental study on the supplementation of slow-release urea to the reserve dairy cattle,yak and beef cattle showed that the feed intake decreased and the growth performance was affected when 2% of slow-release urea was added to the diet of the dairy heifers.But the yaks and beef cattle were not affected.Dairy heifers,yaks and beef cattle obtained the highest daily gain when the proportion of sustained-release urea was 1%.By using in vitro fermentation technology,four levels of slow-release urea were added into diet.It was found that when the proportion of slow-release urea was 1%,the degradation rate of rumen liquid substrates and volatile fatty acid content in fermentation broth were significantly increased,and methane production was significantly decreased.Therefore,considering the economic and environmental benefits,the optimum proportion of slow-release urea added in the diet of dairy heifers,beef cattle and yak was1% of the dry matter in the diet. |
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