| Bile acid,which is mainly synthesized in the liver and stored in the gallbladder,is the major component of bile.Bile acid participates in regulation of glucose and lipid homeostasis through its receptors.For example,bile acid can inhibit bile acid synthesis,reduce triglyceride and cholesterol synthesis and regulate glucose metabolism through binding to farnesoid X-activated receptor(FXR)as well as regulating energy homeostasis in adipose and muscle tissue through the activation of Takeda G-protein-couplcd receptor 5(TGR5).In pig farms,bile acid is used as a feed additive for weaning piglets to promote feed intake,increase average daily gain and improve intestinal health.However,it is unclear whether maternal bile acid supplementation could have effects on skeletal muscle in offspring piglets.Therefore,we aimed to explore the effects of maternal bile acid supplementation during late gestation and lactation on the muscle growth and intramuscular fatetab molism in the longissimus dorsi(LD)muscle of the weaning piglets.1.Effects of maternal bile acid supplementation during late gestation and lactation in the LD muscle growth in weaning pigletsIn this study,thirty Landrace × Large White crossbred sows at the 90 days gestation were randomly divided into two groups.One is the control group(Con)feeding normal diets during the later gestation and lactation;another is the bile acid group(BA)feeding normal diets with 100 mg/kg of bile acids.The experiment was finished at the 21-day of sow breastfeeding.The piglets were weighed,and one male piglet whose weight was closed to the average level was selected from each litter of piglets.After slaughter,the serum and LD muscle were collected.The contents of nuclear acid and protein in the LD muscle of piglets were determined,and the contents of total amino acid in the colostrum of sow and the serum of weaning piglets were detected.It was shown that maternal bile acid supplementation during late gestation and lactation significantly increased the average body weight of weaning piglets(p<0.01),and significantly increased the content of protein in the LD muscle of weaning piglets(p<0.05).Besides,the levels of serum hormones related to animal growth and stress were determined by the radioimmunoassay in weaning piglets.It was shown that maternal bile acid supplementation during late gestation and lactation significantly reduced the contents of cortisol in serum of weaning piglets(p<0.05).Fluorescence real-time quantitative PCR and Western Blot(WB)was used to determine the expression of genes related to protein synthesis,degradation and muscle fiber typing at mRNA and protein levels in the LD muscle of weaning piglets.It was shown that maternal bile acid supplementation during late gestation and lactation significantly decreased the levels of glucocorticoid receptor(GR,p<0.01),besides,the protein expression of autophagy related 7(Atg7,p<0.1)had a decreasing trend.For muscle fiber typing,maternal bile acid supplementation during late gestation and lactation significantly increased the gene expression of myosin heavy chain Ⅱx(MyHC Ⅱx,p<0.05),while significantly decreased the protein expression of myosin heavy chain Ⅰ(MyHC Ⅰ,p<0.05).These results indicated that maternal bile acid supplementation at the dose of 100 mg/kg during late gestation and lactation could increase the protein deposition in the LD muscle of weaning piglets.2.Effects of maternal bile acid supplementation during late gestation and lactation on intramuscular fat metabolism in LD muscle of weaning piglets.Maternal bile acid supplementation during late gestation and lactation significantly decreased the content of triglyceride(p<0.05)in the LD muscle in weaning piglets,which was consistent with the result of oil red O staining.Gas chromatography was performed to determine the fatty acid composition in the LD muscle.It was shown that maternal bile acid supplementation during late gestation and lactation significantly increased the contents of C22:0(p<0.05),C20:3n-3(p<0.05)and C22:2(p<0.05),and significantly decreased the content of C20:3n-6(p<0.05),and the total PUFA(p<0.1)had a increase trend.Furthermore,the concentration of total bile acid in colostrum and sow’s serum and offspring’s serum was determined by a total bile acid detection kit.Also,the protein levels of bile acid receptors were detected by WB.No significant difference was observed in the concentration of total bile acid by sow bile acid administration,and only a decrease trend was observed in the protein content of FXR(p<0.1),Finally,the expression of genes involved in fat acid synthesis,lipolysis,β oxidation and mitochondrial function were detected by realtime-PCR and WB.It was shown that maternal bile acid supplementation during late gestation and lactation significantly decreased the protein expressions of Acyl-CoA synthetase long chain family member 1(ACSL1,p<0.05)and peroxisome proliferator-activated receptor gamma coactivator 1-α(PGC1α,p<0.05),but increased the protein expression of mitogen-activated protein kinase(AMPK,p<0.1),besides,had no significant effect on the expression of genes and proteins related to lipolysis and fatty acid βoxidation.These results suggested that maternal bile acid supplementation at the dose of 100 mg/kg in late gestation and lactation reduces the deposition of intramuscular fat in the LD muscle of weaning piglets. |
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