Effects Of Grape Seed Proanthocyanidins On Productive Performance And Antioxidant Function Of Liver And Intestine In Meat Rabbits

With the improvement of living standards,people have higher requirements for healthy diet.Rabbit meat,with its outstanding advantages,is deeply loved by people,and its consumer market expands year by yea.On the other hand,meat rabbits are highly stressed animals,which are prone to oxidative stress during breeding,leading to decreased performance and diarrhea,and even death in severe cases.In the past breeding process,the use of antibiotics can improve this situation to a great extent,but with the implementation of the national comprehensive anti-resistance policy,the development of rabbit husbandry faces great problems.Therefore,it is urgent to find a safe and effective alternative to antibiotics.Grape seed proanthocyanidins are a class of natural polyphenolic substances with strong antioxidant effects,which have been widely used in a variety of livestock and poultry with good results.In this study,grape seed proanthocyanidins were used as additives in the diet of meat rabbits to explore the effects of grape seed proanthocyanidins on the performance of meat rabbits,and to explore the protective effects of grape seed proanthocyanidins on the intestine and liver by establishing oxidative stress model.In addition,the underlying mechanism of its antioxidant effect was further explored by in vitro cell experiments.The research content is as follows:（1）Effect of grape seed procyanidins on production performance of meat rabbitsIn the experiment,96 weaned meat rabbits with similar body conditions were randomly divided into 4 groups,with 6 replicates in each group,with 4 meat rabbits in each replicate.They were:control group（basic diet）,low dose group（200 mg/kg GSPE）,medium dose group（400 mg/kg GSPE）,and high dose group（800 mg/kg GSPE）.The results showed that compared with the control group,the addition of grape seed proanthocyanidins to the diet had no significant effect on the carcass weight,daily feed intake,and daily weight gain of meat rabbits（P>0.05）,and had no significant effect on slaughter performance（P>0.05）;However,the medium dose group can significantly reduce the feed weight ratio and liver specific gravity of meat rabbits（P<0.05）,and has a significant reduction in serum total cholesterol（P<0.05）.This indicates that adding 400 mg/kg GSPE to the feed can improve the production performance of meat rabbits to a certain extent.（2）Establishment of a model of oxidative stress induced by hydrogen peroxideSixty-four meat rabbits with similar body conditions were selected and randomly divided into 4 groups,with 8 replicates in each group,with 2 meat rabbits per replicate.They were:control group,physiological saline group,low dose group（5%H₂O₂）,high dose group（10%H₂O₂）.From the perspective of growth performance,intraperitoneal injection of hydrogen peroxide could significantly reduce daily weight gain and significantly increase the weight ratio of meat rabbit feed（P<0.05）,while the high dose group could significantly reduce meat rabbit weight gain and daily feed intake.From the perspective of serum biochemical indexes,hydrogen peroxide injection could significantly increase the content of serum alanine aminotransferase,lactate dehydrogenase and alkaline phosphatase（P<0.05）.The content of aspartate aminotransferase was significantly increased,and it was more significant in the high-dose group（P<0.05）.From the perspective of oxidation indicators,the high-dose group can significantly increase the content of malondialdehyde in serum（P<0.05）.It can be concluded that both the low dose group and the high dose group can lead to oxidative stress in meat rabbits,while the effect of the high dose group is more significant.Therefore,the high dose group is used as the standard for subsequent trials.（3）Effects of grape seed procyanidins on intestinal development,liver damage,and antioxidant indexes in oxidative stressed meat rabbitsSeventy-two weaned meat rabbits with good growth status and similar physical condition were randomly divided into three groups,with six replicates in each group,and four meat rabbits per replicate.They were the control group,the hydrogen peroxide injection group（10%H₂O₂）,and the proanthocyanidin and hydrogen peroxide group（200 mg/kg GSPE+10%H₂O₂）.The results showed that compared with the control group,grape seed procyanidins had no significant effect on the intestinal villus height,but could alleviate the decrease in duodenal villus height caused by oxidative stress（P<0.05）;It can significantly reduce the depth of duodenal and jejunal crypts and alleviate the increase in crypt depth caused by oxidative stress（P<0.05）.It can significantly reduced the ratio of intestinal villi height to crypt depth（P<0.05）;From the perspective of oxidation indicators,grape seed proanthocyanidins can significantly reduce the increase in malondialdehyde content in the jejunum and ileum caused by oxidative stress;However,there was still a significant difference compared to the control group（P<0.05）;It can significantly improve the decrease of superoxide dismutase content in the ileum and duodenum caused by oxidative stress（P<0.05）,and can significantly improve the decrease of catalase content in the small intestine caused by oxidative stress（P<0.05）;It can significantly improve the reduction of glutathione peroxidase content in the duodenum and jejunum caused by oxidative stress（P<0.05）,and also has an improvement effect on the ileum,but not significantly（P>0.05）.From the perspective of liver injury,the liver cells in the control group had a complete structure,clear nuclei located in the center of the cells,orderly arrangement between cells,and could connect with each other to form liver cords;Oxidative stress leads to morphological swelling of hepatocytes,vacuolization,inconspicuous intercellular spaces and hepatic cords,and displacement or even disappearance of nuclei.Grape seed proanthocyanidins can significantly improve liver damage caused by oxidative stress.From the perspective of liver antioxidant indicators,grape seed proanthocyanidins significantly improved the reduction of liver superoxide dismutase and catalase content and the increase of malondialdehyde content caused by oxidative stress（P<0.05）.（4）Antioxidant mechanism of grape seed proanthocyanidinsIn order to further explore the antioxidant pathway of grape seed proanthocyanidins,a series of in vitro experiments were conducted using rabbit primary cells as materials.Before the formal test,conduct a preliminary test to determine the appropriate treatment concentration and time for grape seed proanthocyanidins and hydrogen peroxide,which are respectively treated with 200μmol/L GSPE for 4 h,and 100μmol/L H₂O₂for 1 h.The experiment was divided into three groups,namely,the control group,H₂O₂group,and GSPE+H₂O₂group.The results showed that grape seed proanthocyanidins could significantly increase the decrease in antioxidant enzyme content and gene expression level caused by hydrogen peroxide（P<0.05）,improve cell proliferation activity,and reduce cell ROS level.Compared with the control group,grape seed proanthocyanidins significantly reduced the content of Keap1 protein and significantly increased the expression of Nrf2 protein（P<0.05）;Hydrogen peroxide can increase the level of Nrf2 protein to a certain extent,but not significantly（P>0.05）;In terms of gene expression,hydrogen peroxide and grape seed procyanidins had no significant effect on the expression of Keap1 gene（P>0.05）;Grape seed procyanidins significantly increased the expression of Nrf2 gene（P<0.05）.In summary,grape seed proanthocyanidins could improve the performance of meat rabbits,promote the development of small intestine,alleviate oxidative stress-induced liver damage,and enhance the antioxidant capacity of the liver and intestine.Cell experiments showed that grape seed proanthocyanidins could reduce the protein level of Keap1 and increase the expression of Nrf2 protein,thereby activating the expression of downstream antioxidant genes and playing an antioxidant effect.