Effects And Mechanisms Of Dietary Supplementation With Taurine On Lactation Performance Of Gilts

Reduction of lactation performance has been one of the most prominent limiting factors of modern swine production.Excessive oxidative stress and mammary dysplasia during late gestation and lactation compromises the subsequent lactation performance of sows.It is therefore essential to devise nutrition strategies that will optimize sows lactation performance that needs consideration are oxidative stress and mammary development.Previous research in our laboratory concluded that supplementation with antioxidant of isoflavones and plant extracts increases milk yields and milk quality,and therefore induces subsequent lactation performance.Taurine is an established osmoregulator and indirect regulator of oxidative stress,but its use as a maternal food supplement for sow to increased lactation performance by relieve oxidative stress and promote mammary gland development is still not widespread or well understood.Therefore,the objectives of this study were to investigate the roles and potential mechanism of taurine on lactation performance in sows.The main contents and results are presented as follows:Experiment 1 Effects of dietary taurine supplementation to gilts on lactation performanceOne hundred gilts were randomly allocated to the Con（basal diet）and Tau（basal diet with 1%Taurine）groups from 90 D of gestation to weaning,each group contained 50 gilts.The results showed that:（1）No significant effect was observed for the total number of piglets born,average individual weight and litter weight at birth between the two treatment groups（P>0.05）,however,supplemental taurine increased the number of piglets born alive and the piglet weight at weaning,litter weight and average daily gain（P<0.05）at day 21 of lactation.（2）Supplemental taurine increased the lactoprotein content（P<0.05）at the colostrum.No significant effect was observed for the milk fat,lactose,total solids and non-fat solids（P>0.05）in colostrum and milk.The results demonstration that taurine can affect colostrum.（3）Supplemental taurine had an increased IGF-1 and prolactin contents in plasma on day 1 and 10 of lactation,however,treatment had no effect on insulin,glucose,cholesterol,urea nitrogen,triglycerides（P>0.05）.Supplemental taurine increased the content of IGF-1 content of milk on day 1 and 10 of lactation（P<0.05）.（4）Supplemental taurine had an increased taurine content（P<0.05）in plasma and milk on day 1 and 10 of lactation.Meanwhile,supplemental taurine increased the contents of glutamate and arginine（P<0.05）.The results demonstration that taurine can affect amino acid content.（5）Supplemental taurine led to significantly lower（P<0.05）MDA content in plasma and milk on day 10 of lactation,meanwhile,supplemental taurine had a higher antioxidant index including T-SOD,T-AOC,and GPx activities（P<0.05）in colostrum.The results demonstration that taurine can relieve oxidative stress of gilt.Experiment 2 Study on the mechanism of dietary taurine supplementation in improving lactation performance of giltsThis study aimed to investigate the effect of dietary taurine on the oxidative stress and development of gilt mammary gland.Sixteen gilts were randomly allocated to the Con（basal diet）and Tau（basal diet with 1%Tau）groups from 75 D of gestation to weaning,each group contained 8 gilts.The results showed that:（1）Although supplemental taurine did not have a significant effect（P>0.05）on loss of weight,backfat thickness,and average individual weight of piglets,but supplemental taurine had a higher feed intake and milk yield（P<0.05）during lactation period,meanwhile the piglet weight at weaning（P<0.05）at day 21 was increased.（2）Supplemental taurine had increased IGF-1 contents（P<0.05）in plasma and milk on day 1 and 10 of lactation.Meanwhile,the lactoprotein content was significantly higher（P<0.05）at the colostrum.（3）Supplemental taurine led to significantly lower（P<0.05）MDA content in plasma and milk on day 1 and 10 of lactation,meanwhile,antioxidant index including T-SOD,T-AOC,and GPx activities（P<0.05）in plasma and milk were higher.（4）Supplemental taurine had a decreased MDA contents（P<0.05）and increased T-AOC activity（P<0.05）in mammary tissue on day 1 and 21 of lactation,Meanwhile,the protein expression levels of Nrf2,NQO-1 and Txnrd1（P<0.05）,related to antioxidants increased in the mammary tissue on day 21 of lactation.The results demonstration that taurine can relieve oxidative stress of mammary gland in gilt.（5）Supplemental taurine had a greater diameter of alveolar（P<0.05）and DNA and protein contents（P<0.05）in mammary tissue on day 1 and 21 of lactation.Meanwhile,the protein expression levels of Cyclin D1 and STAT5（P<0.05）,related to cell proliferation increased in the mammary tissue on day 21 of lactation.The results demonstration that taurine can promote mammary gland development.（6）Supplemental taurine increased the protein expression levels ofβ-casein（P<0.05）,related to m TOR signaling pathway（p-m TOR,p-S6）in the mammary tissue on day1 and 21 of lactation.（7）Supplemental taurine increased T-SOD,T-AOC and GPx activities and decreased MDA content（P<0.05）in the jejunum in the piglets at day 1,7 and 21 of post-birth compared with Con group.Furthermore,piglets in the Tau group had higher villus height and villus height-to-crypt depth ratio（VCR）,ZO-1 protein expression（P<0.05）,and secretory immunoglobulin A（s Ig A）content（P<0.05）in the jejunum,which improved intestinal morphology and barrier function.Experiment 3 Study on the mechanism of taurine relieving oxidative stress of mammary epithelial cellsThe Tau supplementation during late gestation and lactation of gilts alleviated the oxidative stress in the mammary gland of gilts,and increased antioxidant index in the milk,promoted the growth performance of the piglets.This study was conducted to investigate molecular mechanism of the cytoprotective effects of taurine against oxidative stress using the porcine mammary epithelial cells（PMEC）.The PMEC were pretreated with oxidative injury induced by hydrogen peroxide（H₂O₂）and followed by taurine,Nrf2 Si RNA and inhibitor of MAPK.PMECs were collected for determining ROS production and related protein expression levels.The results showed that:（1）Compared to 0μM H₂O₂ group,500μM H₂O₂ group decreased cell viability（P<0.05）and T-SOD activity（P<0.05）,increased ROS production（P<0.05）.The model of oxidative stress was successfully established.（2）Taurine significantly increased H₂O₂-induced cell death（P<0.05）,protect the T-SOD activity（P<0.05）and block the ROS production（P<0.05）.The rescuing on the cell viability and cell cycle were dismissed after in Nrf2 Si RNA transfected PMEC.The results demonstration that taurine can block ROS production through Nrf2 signaling pathway.（3）Compared to alone H₂O₂ group,taurine culture prior to the H₂O₂ exposure significant increased antioxidant defense genes and proteins,including Nrf2,x CT,NQO-1,HO-1（P<0.05）.The rescuing on the antioxidant defense proteins expression,including Nrf2,HO-1,NQO-1,Txnrd and x CT were dismissed after in Nrf2 Si RNA transfected PMEC.The results demonstration that taurine can relieve oxidative stress through Nrf2signaling pathway.（4）Compared to alone H₂O₂ group,taurine culture prior to the H₂O₂ exposure significant decreased ER stress genes and proteins expression,including CHOP and GRP78.The rescuing on the ER stress proteins expression was dismissed after in Nrf2Si RNA transfected PMEC.The results demonstration that taurine can relieve ER stress through Nrf2 signaling pathway.（5）Compared to alone H₂O₂ group,taurine culture prior to the H₂O₂ exposure significant increased phosphorylation levels of ERK1/2,JNK1/2 and P38.Using selective inhibitors the results showed that the protein expression decreased of Nrf2,HO-1 and Txnrd1.The results demonstration that taurine can relieve oxidative stress through MAPK-Nrf2 signaling pathway.Experiment 4 Study on the mechanism of taurine in mammary cell proliferationExperiment 1 and 2 confirmed that dietary Tau supplementation in gilts during late gestation not only significantly decreased oxidative stress and promote mammary development and milk secretion.So,this experiment was to investigate the taurine and its molecular mechanism in regulating cell proliferation in PMEC.The study using different concentrations of taurine（0-2 mM）combined with m TOR-specific inhibition of treated PMEC.The results showed that:（1）Compared to Con group,1.2 mM taurine group increased cell viability（P<0.05）and percentage of cells in the G2 and S phases（P<0.05）.Treated with the m TOR inhibitor resulted in a marked reduction in the cell viability.The results demonstration that taurine can promote cell proliferation through m TOR signaling pathway.（2）The protein and gene expression of Cyclin D1 and m TOR signaling pathway relative protein phosphorylation levels were significantly increased significantly increased in PMEC treated with 1.2 mM taurine than control group.Treated with the m TOR inhibitor resulted in a marked decreased in the protein expression of Cyclin D1 and m TOR signaling pathway.（3）Exposure of PMEC to 1.2 mM taurine was significantly inhibited cell apoptosis under normal or oxidative stress condition.Compared to Con group,1.2 mM taurine group decreased gene and protein expression bax（P<0.05）and increased Bcl2（P<0.05）.（4）Compared to alone H₂O₂ group,1.2 mM taurine group increased protein expression of Bcl2 and decreased Bax.The rescuing on the protein expression was dismissed after in Nrf2 Si RNA transfected PMEC.The results demonstration that taurine can inhibite cell apoptosis through Nrf2 signaling pathway.In conclusion,our research demonstrated that appropriate improved dietary taurine levels to gilts during late gestation and lactation significantly increased lactation performance by improved development of mammary gland and relieving oxidative stress.Dietary taurine relieving oxidative stress and promote the mammary development in porcine mammary glands via activation of the MAPK/Nrf2 and m TOR/Cyclin D1signaling pathway,respectively.