| Maternal nutritional challenges,especially during critical periods of gestation,lead to permanent changes of foetal gene and protein expression via DNA methylation.These alterations in DNA methylation can persist throughout the life of the organism,and consequently,exert long-term effects on offspring growth,development,and disease susceptibility later in life.However,in sow production,it is still unclear whether DNA methylation mediates the effect of maternal nutrition during gestation on the growth performance and muscle development of the offspring.Therefore,four experiments were conducted to evaluate the effect of maternal nutrition during gestation on the growth performance and meat quality of the offspring pigs and the regulatory effect of DNA methylation.The experimental results were presented as following.Exp.l Effect of dietary nutrient levels during gestation on the growth performance and carcass quality of the offspring pigs.A total of 33 Landrace-Yorkshire crossbred primiparous gilts were used in this study.After insemination,gilts were randomly assigned to one of three groups(n = 11)with different nutrient levels:low(LN),medium(MN),and high(HN)nutrient level group.The gilts in MN group were provided 100,125,and 150%of the energy requirement for maintenance during early,mid,and late gestation,respectively.The gilts in LN and HN group received 75%and 150%of the MN intake in all the stage of gestation,respectively.After parturition,all the gilts received the same diet and fed ad libitum until weaning at day 28 of lactation.Sixteen weaning pigs(8 male and 8 female)per group were selected to be reared following the standard feeding regimen with the starter,grower and finisher diets recommended for the breed.All the pigs fed ad libitum until postnatal day 189.At day 0,28,and 189,typical pigs were selected for sacrifice and samples were collected.The results were presented as following.(1)The litter birth weight of piglets was lower in LN group than that in MN group(P<0.05).The feed conversion ratio during day 28 to 189 was lower in LN group than that in MN group(P<0.05).There were no differences of ADFI,ADG,and final marketing body weight between HN and MN group.(2)There were no differences of the carcass body weight,backfat thickness,and loin muscle area in finishing pigs between MN and HN group.(3)Serum glucose concentration was lower at day 0,but was higher at day 152 and 189 in LN pigs than that in MN pigs(P<0.05).Serum insulin concentration was higher at day 131 and 189 in LN pigs than that in MN pigs(P<0.05).During intravenous glucose tolerance tests(IVGTT),the area under the blood glucose curve(AUC)was significantly increased,whereas glucose clearance rate was significantly decreased in LN pigs as compared with MN pigs(P<0.05).No difference was observed in serum glucose and insulin concentration,as well as the AUC and glucose clearance rate during IVGTT between MN and HN group.(4)The lactate content was lower at day 0,but the glycogen content was higher at day 152 and 189 in the LD muscle of LN pigs than those in MN pigs(P<0.05).The muscle lactate and glycogen content were not difference between MN and HN group.(5)The gene expression of glucose transporter-4(GLUT4)was low at day 0,28,and 189,and the protein expression of glucose transporter-4 was low at day 0 and 189 in the LD muscle of LN pigs than that in MN pigs(P<0.05).(6)The methylation level(day 0 and 189)at the GLUT4 promoter was significantly increased in the LD muscle of LN pigs than that in MN pigs(P<0.05).The gene expression of DNA methyltransferase1(DNMT1,day 0 and 28),DNMT3a(day 189),DNMT3b(day 0)as well as the betaine-homocysteine methyltransferase(day 189)was significantly higher in the LD muslce of LN pigs than those in MN pigs(P<0.05).(7)The gene expression of insulin receptor(day 0 and 189),insulin substrate-1(day 28),phosphatidylinositol 3-kinase(day 28)and protein kinases 2(day 0)was significantly lower in the LD muslce of LN pigs than those in MN pigs(P<0.05).(8)The gene expression of lactate dehydrogenase(day 0 and 189)and pyruvate dehydrogenase kinase(day 189)was higher,whereas the gene expression of hexokinase(day 189),pyruvate kinase(day 28),glycogen synthetase(day 28 and 189)and citrate synthase(day 28)was lower in the LD muslce of of LN pigs than those in MN pigs(P<0.05).Collectively,the offspring born to HN sows had a similar growth performance with the offspring born to MN sows.However,the feed converation ratio was decreased in the offspring born to LN sows as compared with MN sows.These changes may be related to DNA methylation in the skeletal muscle.Exp.2 Effects of maternal methyl donor supplementation during gestation on the reproductive performance of sows and growth performance of nursing pigs.A total of 64 Landrace × Yorkshire crossbred sows(initial body weight 211.14 ± 2.57 kg)equally balanced by parity(3 and 5)were artificially inseminated upon observation of oestrus with the pooled semen obtained from two littermate boars.After insemination,sows were randomly assigned to receive one of four diets(n = 16)during gestation:control diet(CON);control diet supplemented with methyl donor(MET);control diet supplemented with bisphenol A(BPA);and control diet supplemented with BPA and MET(BPA + MET).CON sows were fed a basal diet which completely met the recommendations of the National Research Council.A MET-supplement premix was added to the control diet containing 3 g kg-1 betaine,400 mg kg-1 choline,15 mg kg-1 folic acid,and 150 ?g kg-1 vitamin B12.Sows fed the BPA diet were supplemented with 50 mg kg-1 diet of bisphenol A.Sows were assigned to dietary treatments immediately after completion of the final artificial insemination,and treatments were administered throughout gestation.The results were presented as following.(1)The individual piglet weight at birth and weaning,and the litter weight at weaning was higher in MET group than those in CON group(P<0.05).(2)Maternal methyl donor supplementation significantly increased plasma methionine content of sows at day 90 of gestation,decreased plasma cysteine and urea content of sows at day 90 of gestation,and increased plasma methionine content of newborn piglets(P<0.05).(3)Maternal methyl donor supplementation significantly decreased plasma homocysteine content of sows at day 30 and 110 of gestation(P<0.05),increased plasma S-adenosylmethionine(SAM)content of sows at day 90 of gestation(P<0.05),and tend to increase the ratio of SAM to S-adenosylhomocysteine(SAH)in the plasma of sows at day 90 of gestation(P = 0.08).(4)Maternal methyl donor supplementation significantly increased plasma SAM content of newborn piglets(P<0.05).Collectively,our results indicated that maternal methyl donor supplementation during gestation increased piglets' birth weight and improved piglets' growth performance during lactation.There changes may be related to the decreased plasma homocysteine level of sows and increased plasma SAM content of newborn piglets.Exp.3 Effects of maternal methyl donor supplementation during gestation on the growth performance and muscle development of offspring pigs.In sows,the experimental design was same to Exp.2.After weaning,six litters with 9-11 piglets per litter were selected,and all littermates with a weight approximating the mean of all litter weights within the treatment were reared until the finishing stage(approximately 110 kg·BW).Pigs were euthanised at newborn(day 0),weaning(day 28),and finishing(110 kg·BW)stage,and samlpes were collected.The results were presented as following.(1)Pigs in MET group exhibited a greater ADG during day 28 to 180 and final body weight at day 180 than pigs in CON group(P<0.05).Serum IGF1 content was significantly increased at newborn(P<0.05),weaning(P<0.05),and finishing stage(P =0.08)in MET group than that in CON group.The gene expression of IGF 1 in the liver was down-regulated at newborn(P<0.05),weaning(P<0.05),and finishing stage(P = 0.07),and the gene expression of STAT5b in the liver was down-regulated at finishing stage(P<0.05)in MET pigs than those in CON pigs.Compared with CON pigs,the gene expression of IGF1 receptor was significantly lower at newborn and weaning stage in the LD muscle of MET pigs(P<0.05).The protein expression of IGF 1 in the liver was down-regulated at newborn(P<0.05)and finishing(P = 0.07)stage,and the protein expression of IGF1 receptor in the LD muscle was down-regulated at newborn stage(P<0.05)in MET pigs than those in CON pigs.Compared with CON pigs,the methylation level at the IGF1 promoter was upregulated in the liver of MET pigs at newborn and finishing stage,which was accompanied by evelated the gene expression of betaine-homocysteine methyltransferase(P<0.05).(2)Maternal methyl donor supplementation significantly increased the weight of longissimus dorsi,semitendinosus,and gastrocnemius muscle at newborn stage,as well as increased the weight of longissimus dorsi muslce at weaning stage(P<0.05).There was a higher muscle fiber area in the LD muscle of MET pigs compared with CON pigs(P<0.05).Compared with CON pigs,the gene expression of MyODl was significantly up-regulated in the LD muscle of MET pigs at newborn,weaning and finishing stage(P<0.05).Consistently,the protein expression of MyODl was higher at newborn stage(P<0.05),and tend to be higher(P = 0.08)in the LD muscle of MET pigs than that in CON pigs.Compared with CON pigs,a greater methylation level was observed in the CpG10 and CpG13-14 site at newborn stage,and in the CpG8 and CpG19-21 site at finishing stage at the MyOD1 promoter of MET pigs(P<0.05).These alterations in methylation concurred with increased gene expression of methionine adenosyltransferase,methionine synthase,and adenosylhomocysteinase in the LD muscle of newborn pigs(P<0.05).(3)Pigs in MET group exhibited an evelated MyHC ?b gene expression in the LD muscle at newborn and finishing stage as compared with pigs in CON group(P<0.05).The Fast-MyHC protein expression was higher in the LD muscle of MET pigs at newborn stage as compared with CON pigs(P<0.05).Compared with CON pigs,MET pigs exhibited a greater methylation level in the CpG2 site of muscle MyHC ?b promoter at newborn stage,and had a greater methylation level in the CpG3 and CpG6 site of muscle MyHC ?b promoter at finishing stage(P<0.05).Collectively,our results indicated that maternal methyl donor supplementation during gestation increased hepatic IGF1 and muscle MyOD1 protein expression of offspring likely through DNA methylation.These alterations in methylation can persist from birth to the adult with long-term consequences on muscle growth and develoment,which then promoted growth performance in later life.Exp.4 Effects of maternal methyl donor supplementation during gestation on the bdoy composition and carcass quality of offspring pigsThe experimental design was same to Exp.3.The results were presented as following.(1)Prenatal BPA exposure increased the subcutaneous fat as well as adipocyte diameter of finishing pigs(P<0.05).At weaning stage,BPA-pigs had higher mRNA level of LPL,FAS,SCD and ELOVL6 in subcutaneous fat than CON-pigs.At finishing stage,the mRNA level of FAS and SCD in subcutaneous fat was higher in BPA-pigs than CON-pigs(P<0.05).The average methylation level at the FAS and SCD promoter was significantly lower in BPA pigs at birth and the finishing stage than CON pigs(P<0.05).(2)The muscle a*value was higher and glycogen content was lower in MET pigs than those in CON pigs(P<0.05).The mRNA level of glycogen synthase(GS)was downregulated in the LD muscle of MET pigs at birth(P = 0.09)and the finishing stage(P<0.05)in comparison with CON pigs.Compared to CON pigs,the average methylation level in MET pigs at the GS promoter was significantly increased at birth and the finishing stage(P<0.05).Gestational exposure to BPA reduced the dressing percentage and muscle pH values,but increased muscle lactate content,lactate dehydrogenase enzyme activity,glycolytic potential and L*values in offspring pigs(P<0.05).The mRNA level of LDH was upregulated in the LD muscle of BPA pigs at birth(P<0.05)and the finishing stage(P<0.05)in comparison with CON pigs.Compared with CON pigs,the average methylation level at the LDH promoter was significantly decreased in BPA pigs at birth and the finishing stage(P<0.05).Collectively,our results indicated that gestational exposure to BPA increased the subcutaneous fat of offspring via evelated lipids synthesis,and impaired meat quality of offspring via evelated lactate accumulation.Maternal methyl donor supplementation during gestation improved meat quality of offspring via impaired glycogen synthesis.In conclusion,our results indicated maternal overnutrition during gestation had a limited effect on the growth performance of offspring pigs.Maternal undernutrition impaired offspring glucose torelance,which contributed to the reduced feed conversion ratio of postweaning pigs.On the other hand,maternal methyl donor supplementation during gestation promoted hepatic IGF1 secretion and increased muscle MyOD1 protein expression of offspring,which contributed to improve offspring growth performance and muscle development in later life.Gestational exposure to BPA increased the subcutaneous fat of offspring via evelated lipids synthesis,and impared meat quality of offspring via evelated lactate accumulation.Importantly,DNA methylation remarkably mediates the effects of maternal nutrition during gestation on the offspring growth performance and meat quality. |
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