Abstract:

This experiment aimed to study the effects of substitution of different levels of urea for natural protein on haematological indices，serological parameters and the histopathology of digestive organs in mutton sheep and provide basis for the safe use of urea.Sixty four Dorper×thin-tailed Han crossbred male lambs with average body weight of (30.77±0.02)kg were randomly divided into 4 treatments as follows：control group and control group supplemented with 0.5%，1.5%，and 2.5% urea,respectively.The investigation lasted for 63 days including 21 days of adaptation.Each treatment including 8 sheep and blood was sampled on d 1 and d 42.Thirty two lambs were slaughtered at the end of the experiment，and the sample of duodenum，rumen，liver and kidney were taken for pathological examination.The detection results of haematological indices showed that the platelet count of 1.5% and 2.5% urea group were significant higher than that of the control group and 0.5% urea group (P<0.05)；the mean corpuscular hemoglobin concentration of 2.5% urea group was also remarkably higher than that of 0.5% urea group (P<0.05)；average red blood cell hemoglobin content of 2.5% urea group was higher than that of other 3 groups (P<0.05).Blood urea nitrogen of 1.5% and 2.5% urea groups were significant lower than that of control and 0.5% urea group (P<0.05).However，the effect of urea supplementation on triacylglycerol was opposite to the results of blood urea nitrogen (P<0.05)；the concentration of glutamate pyruvate transaminase，glutamic-oxaloacetic transaminase，creatinine total bilirubin and blood ammonia in 2.5% urea group were the highest among the 4 groups (P<0.05)，but the concentration of alkaline phosphatase of 2.5% group was lower than that of control group (P<0.05)；the rest indices of serological parameters were not remarkably different among different groups (P>0.05).The lesion of kidney of 2.5% urea group was more serious than that of other groups (P<0.05).These results indicated that，the haematological indices，serological parameters and the main digestive organs of sheep were not significantly affected when the level of urea in ration under 1.5%.However，the health of mutton sheep will be seriously harmed as the supplementation of urea increased to 2.5% in feed.