Effects Of Different Forms Of Zinc Oxide On Growth Performance,Gastrointestinal Physiology And Content Of Trace Element In Meat Rabbits

Zinc is one of the essential trace elements for the animals.It plays an important role in maintaining animal growth and intestinal health.Zinc oxide（ZnO）is one of the sources of zinc in animal feed,and different forms of ZnO have different effects on animals.In this study,the effects of feed grade zinc oxide（F-ZnO）,nano zinc oxide（N-ZnO）and coated zinc oxide（C-ZnO）on growth performance,digestive physiology and tissue trace element content of meat rabbits was studied.Four treatment groups were set up.The form and level of zinc oxide were F-ZnO（120mg/kg）,N-ZnO（120 mg/kg）,C-ZnO（120 mg/kg）and high-dose zinc oxide（T-ZnO,2000 mg/kg）.A total of 216 New Zealand white rabbits were randomly assigned to 4treatments,27 replicates in each treatment and 2 rabbits in each replicate.This experiment was last for 42 days,1-21d was the pre-test period,22-42d was the post-test period.The growth performance,gastrointestinal physiology and tissue antioxidation capacity and tissue trace element content of meat rabbits were measured.The results showed as follows:（1）There was no significant difference in average daily gain（ADG）,average daily feed intake（ADFI）and feed/gain（F/G）between the treatments in the pre-test period（P>0.05）.Compared with F-ZnO,N-ZnO,C-ZnO and T-ZnO significantly improved ADG of meat rabbits in the post-test period（P<0.05）.The diarrhea rate,mortality rate and health risk index of rabbits in C-ZnO group decreased by 45.46%,9.99%and 28.73%（P>0.05）,respectively,compared with F-ZnO.（2）There was no significant difference in serum total protein,albumin,globulin,glucose,triglyceride,alanine aminotransferase,aspartate aminotransferase and lactate dehydrogenase among the four groups（P>0.05）.However,N-ZnO significantly increased the alkaline phosphatase activity in serum of rabbits at the end of the test（P<0.05）.N-ZnO and C-ZnO significantly increased the height of villi,decreased the depth of crypt and increased the ratio of villi to crypt in duodenum and ileum（P<0.05）,and upregulated the m RNA expression of cluadin-1,TJP-1,TJP-2 at 22 d of the test and that of occludin at 42 d of the test（P<0.05）.（3）The cellulase activity in the cecum of meat rabbits in N-ZnO group was higher than that in F-ZnO group（P<0.05）.Compared with F-ZnO and N-ZnO,the content of ammonia nitrogen（NH₃-N）in the cecum in C-ZnO group was higher（P<0.05）,and there was no significant difference between T-ZnO and C-ZnO（P>0.05）.The content of volatile fatty acids（VFA）in the cecum was no significant difference in four groups（P>0.05）.（4）The serum GSH-Px of rabbits in C-ZnO group was higher than that in other groups at 22 d of the test（P<0.05）.And the content of MDA in liver in C-ZnO,N-ZnO and T-ZnO groups was lower than that in F-ZnO groups at 42 d of the test（P<0.05）.（5）On the 22nd day of the experiment,the content of zinc and copper in serum and liver of rabbits were no significant difference in N-ZnO,C-ZnO and F-ZnO group（P>0.05）,but the content of iron in serum in N-ZnO and C-ZnO group was higher than that in F-ZnO group（P<0.05）T-ZnO significantly increased the content of zinc in serum and liver（P<0.05）,but had no significant effect on the content of iron and copper（P>0.05）.On the 42nd day,compared with F-ZnO,N-ZnO and C-ZnO could reduce the content of copper in feces.T-ZnO significantly increased the content of zinc in serum,liver,muscle and feces,and decreased the content of iron and copper in feces（P<0.05）.In conclusion,compared with F-ZnO,N-ZnO and C-ZnO can improve the intestinal morphology,antioxidant function,growth performance of meat rabbits,and do not effect the deposition of zinc in the liver and muscle of animals,but may reduce the excretion of copper.Considering the growth performance and antioxidant status of meat rabbit,C-ZnO was better than F-ZnO and N-ZnO.