| The aim of this study is to investigate the effects of adding bile acids(BAs)to weaned-tofinish rabbit diets with different energy levels on production performance,serum biochemical indicators,lipid metabolism,and endogenous bile acid metabolism,as well as to explore the effects and associations of the adenosine monophosphate-activated protein kinase(AMPK)signaling pathway on lipid metabolism and endogenous bile acid metabolism.This experiment employed a 2 × 4 factorial design and selected 384 healthy New Zealand white rabbits,which were randomly divided into 8 experimental groups(with 48 replicates per group,and one rabbit per replicate).The study factors were dietary energy level(basal diet BE with digestible energy:10.25 MJ/kg;HE with digestible energy: 10.75 MJ/kg)and BA supplemental level(0,45,90,145 g/t)in high-energy diets.The pre-feeding period lasted 7 days,and the formal experiment ran for 28 days.Seven days before the end of the feeding experiment,8 rabbits from each group were randomly selected and transferred to metabolic cages for digestion and metabolism experiments.The test results are as follows:(1)Compared with the basic diet,feeding the high-energy diet significantly reduced the feed intake of growing rabbits(P < 0.05),but had no significant effect on average daily gain and feed conversion ratio(P > 0.05).Compared with the group without BAs added to the diet,adding 135 g/t BAs to the diet significantly reduced the feed conversion ratio compared with the control group(P < 0.05).The energy level of the diet and the level of bile acid addition had an interactive effect on the average daily gain of rabbits(P < 0.05).The energy level of the diet and the level of bile acid addition did not have a significant effect on the slaughter performance of the experimental rabbits(P > 0.05),and no interactive effect was found between the energy level of the diet and the level of bile acid addition on the slaughter performance of rabbits(P >0.05).Compared with the basic diet group,the liver weight and liver index of the high-energy diet group experimental rabbits were significantly increased(P < 0.05).In terms of the comprehensive energy level × bile acid level,the liver weight of the HE-45 g/t BAs group and HE-135 g/t BAs group was significantly increased compared with the BE-135 g/t BAs group(P < 0.05).(2)Compared with the basic diet group,feeding the high-energy diet group and bile acid addition group significantly increased the crude fat digestibility(P < 0.05),while the energy level of the diet and bile acid addition had no significant effect on the apparent digestibility of crude protein,neutral detergent fiber,and acid detergent fiber(P > 0.05).Compared with the basic diet group,the serum levels of TG,TCHO,LDL,ALB,and TP were significantly increased in the high-energy diet group(P < 0.05),and there was a trend of bile acid addition affecting HDL(0.1 > P > 0.05),indicating that high concentrations of bile acid addition may decrease HDL in the serum.There was a trend of interactive effect between the energy level of the diet and bile acid addition on the concentration of HDL in the serum(0.1 > P > 0.05).In the follow-up experiment,the basic diet without bile acid addition was selected as the experimental group(BE group),the high-energy diet without bile acid addition was selected as the energy experimental group(HE group),and the diet with 90 g/t bile acid addition was selected as the bile acid control group(BE-BAs,HE-BAs),in order to explore the mechanisms of the effects of dietary energy level and bile acid addition on fat metabolism and endogenous bile acid metabolism in growing rabbits,as well as the effects and connections of the AMPK signaling pathway on fat metabolism and endogenous bile acid metabolism.The experiment found that:(3)Compared with the BE group,the shoulder blade and perirenal fat weight and the deposition rate of shoulder blade and perirenal fat of the rabbits in the HE group were significantly increased(P < 0.05).Adding bile acids to the diet reduced fat deposition,but the difference was not significant(P > 0.05).Compared with the BE group,the FAS enzyme activity of the BE-BAs group and the HE group was significantly increased(P < 0.05),and the LPL enzyme activity of the HE group was significantly decreased(P < 0.05);there was an interactive effect between the energy level of the diet and bile acid addition on FAS enzyme activity(P <0.05).Compared with the BE group,the gene expression of FAS and ACC in the HE group was significantly increased(P < 0.05),while the gene expression of LPL and HSL was significantly decreased.Compared with the BE group and the HE group,the gene expression of ACC in the BE-BAs group and the HE-BAs group was significantly decreased(P < 0.05).Compared with the BE group,the gene expression of HSL in the BE-BAs group was significantly increased(P< 0.05);there was an interactive effect between the energy level of the diet and bile acid addition on HSL expression(P < 0.05).(4)Compared with the BE and HE groups,the serum total bile acid concentration in the BE-BAs and HE-BAs groups was significantly decreased(P < 0.05).In the liver,the total bile acid concentration was significantly increased in the BE-BAs group compared with the BE group(P < 0.05),while it was significantly decreased in the HE-BAs group compared with the HE group(P < 0.05).Compared with the BE group,the expression levels of bile acid synthesisrelated genes(CYP7A1 and CYP27A1)and transporters(BSEP)were significantly increased(P< 0.05),whereas the expression levels of FXR and FGFR4,which are related to the FXR signaling pathway,were decreased,with FGFR4 expression significantly decreased(P < 0.05).The expression levels of CYP7A1 and CYP27A1 in the ileum were significantly increased(P <0.05),as was the expression of the reabsorption transporter ASBT(P < 0.05),in the HE group compared with the BE group.Compared with the BE and HE groups,the expression level of CYP27A1 was significantly decreased(P < 0.05),while that of ASBT was significantly increased(P < 0.05),and the expression levels of FXR and FGF19 were significantly increased(P < 0.05)in the HE-BAs group.Compared with the HE group,the expression level of AMPKα1 was significantly increased(P < 0.05)in the HE-BAs group,and there was an interactive effect of diet energy factors and bile acid supplementation on the gene expression of AMPKα1(P < 0.05).Compared with the BE and HE groups,the protein expression level of P-AMPKα1 was significantly increased(P < 0.05)in the HE-BAs group.In conclusion,a high-energy diet can decrease the feed intake of meat rabbits,lead to increased scapular and perirenal fat deposition,and elevate blood lipid levels.However,dietary BAs can mitigate these effects by influencing enzyme activities related to fat metabolism and m RNA expression of related genes.Following the ingestion of high-energy diets,fat anabolism is accelerated,and bile acid demand is increased,which in turn accelerates bile acid anabolism and transport.The addition of exogenous bile acids to the diet can inhibit bile acid synthesis and promote bile acid transport in meat rabbits. |
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