Effect Of Dietary Supra-nutritional Selenium Supplementation On Lactation Performance Of Multiparous Sows During Summer And Its Underlying Mechanism

Lactating sows have a large amount of metabolism for the synthesis and secretion of colostrum and milk with the requirement of plenty of oxygen,which are prone to generate lots of oxygen free radicals and some lipid peroxides.Supra-nutritional selenium（Se）can improve the milk yield and milk composition of cow and ewe,but the supra-nutritional Se has not been reported in sows.Therefore,perinatal sows and porcine mammary epithelial cells were used as the research objects in vivo and in vitro.The objective of this dissertation was to investigate the effects of dietary supra-nutritional Se supplementation on lactation performance of multiparous sows during summer and its underlying mechanism.This dissertation includes 4 parts as follows:Part 1.Effects of pad-fan cooling and dietary supra-nutritional Se supplementation on lactation performance,colostrum and milk composition of sows during summer.This study was a 2×2 factorial design,where the first factor was farrowing environment（Traditional vs.pad-fan cooling farrowing house）,and the second factor was dietary Se level during late gestation and lactation（0.3 vs.1.2 mg/kg Se as Se-yeast）.Forty multiparous sows（Landrace×Yorkshire）were randomly allotted by parity,body condition and historical reproductive performance to 1 of 4 treatments with 10 sows per treatment.The feeding trial was conducted from day 85 of gestation until day 21 of lactation（weaning）.There was little evidence of interactions of farrowing environment with Se treatments（P>0.10）with the exceptions of nutrient content of colostrum and 7-d milk.Sow reproductive performance and colostrum yield was unaffected by treatments（P>0.10）.Compared with heat-stressed sows,pad-fan cooled sows had greater piglet ADG during the1^st week（P<0.05）,litter weight（P<0.10）and average piglet weight（P<0.10）at 14postpartum.Pad-fan cooled sows had higher ADFI during the 2^nd,3^rd,and 1^st to 3^rd week of lactation（P<0.05）,and higher protein,lactose,solids-not-fat,and ash percentage in 14-d milk（P<0.05）.Compared with the control diet,sows fed supra-nutritional Se had greater piglet preweaning survival（P<0.10）.Also,greater concentrations of protein（P<0.05）,lactose（P<0.05）,solids-not-fat（P<0.05）and ash（P<0.10）in colostrum,and greater concentrations of fat in 7-d and 14-d milk were found for sows fed supra-nutritional Se（P<0.05）.Sows fed supra-nutritional Se had higher plasma Ig A（P<0.05）,Ig G（P<0.10）and Ig M level（P<0.10）at 21d postpartum,and higher Ig A（P<0.10）and Ig M levels（P<0.05）in colostrum,and higher Ig A（P<0.05）,Ig G（P<0.10）and Ig M levels（P<0.10）in21-d milk.Piglets from sows fed supra-nutritional Se had higher plasma Ig A（P<0.05）,Ig G（P<0.10）and Ig M levels（P<0.10）at 1 d postpartum,and higher Ig A（P<0.05）and Ig G levels（P<0.05）at 21 d of age.Pad-fan cooling improved milk composition and lactation performance of sows by increasing sow feed intake during lactation,while maternal supra-nutritional Se supplementation increased piglet preweaning survival via improving colostrum and milk composition,and maternal immunoglobulin transfer.Part 2.Effects of pad-fan cooling and dietary supra-nutritional Se supplementation on Se and antioxidant status of sows,colostrum and milk,and nursing piglets during summer.The Se and antioxidant status of sows,colostrum and milk,and nursing piglets were largely unaffected by environment×dietary Se level interaction（P>0.10）.Compared to sows fed the control diet,sows fed the supra-nutritional Se diet had greater Se content in plasma at farrowing and 21-d post-partum,and in colostrum and 21-d milk,and accordingly,in the plasma of their 1-day-old and 21-day-old nursing piglets（P<0.05）.Pad-fan cooling improved the antioxidant status of sows at farrowing including GSH-Px activity（P<0.10）and GSH content（P<0.10）,while supra-nutritional Se supplementation improved the antioxidant status including GSH-Px activity and MDA content both at farrowing and 21-d post-partum（P<0.05）.For colostrum and milk,pad-fan cooling enhanced GSH content in21-day milk（P<0.10）,while supra-nutritional Se supplementation improved antioxidant status in colostrum（MDA content,P<0.05）and 21-day milk（T-AOC and MDA content,P<0.10）.For nursing piglets,piglets from pad-fan cooled sows had improved antioxidant status at 1-day（GSH-Px activity and GSH content,P<0.05,P<0.10）and 21-days（T-AOC,SOD,GSH and MDA,P<0.10,P<0.05,P<0.10,P<0.05）.Nursing piglets from sows fed supra-nutritional Se had improved antioxidant status including GSH-Px activity and MDA content both at 1-day and 21-days（P<0.05）.In conclusion,results of this research indicate that during heat stress conditions,pad-fan cooling during lactation or perinatal dietary supra-nutritional Se supplementation can improve the antioxidant status of sows,colostrum and milk,and nursing piglets.Part 3.Effects of maternal supra-nutritional Se supplementation on the intestinal antioxidant status and intestinal function of the offspring weaning piglets.This study was conducted as a single factorial design with 2 dietary treatment（0.3 vs.1.2 mg/kg Se as Se-yeast）.The feeding trial was carried out from day 85 of gestation until day 21 of lactation,and all sows were reared in traditional gestating and farrowing house.At 3 d postweaning,6 litters per group were selected,and each piglet were selected from litter for sampling（3 males and 3 females）.After blood samples were collected,piglets were slaughtered,and duodenum,jejunum,ileum were sampled.The results show that:（1）Maternal supra-nutritional Se supplementation enhanced the plasma Se content（P<0.05）and relative weight of small intestine of offspring weaning piglets（P<0.10）.（2）Maternal supra-nutritional Se supplementation increased the SOD activity in duodenum of offspring weaning piglets（P<0.10）,T-AOC and GSH-Px activity in duodenum,jejunum and ileum（P<0.05）,decreased MDA content in duodenum,jejunum and ileum of piglets（P<0.05）.（3）Maternal supra-nutritional Se supplementation upregulated the relative m RNA expression of SEPHS2,SEPP1,GPX1 and TXNRD1 in duodenum,jejunum and ileum of offspring weaning piglets（P<0.05）.（4）Maternal supra-nutritional Se supplementation downregulated the relative m RNA expression of duodenal TNF-α（P<0.05）,IL-6（P<0.05）,IFN-γ（P<0.10）,jejunal TNF-α（P<0.10）,IL-6（P<0.05）,IFN-γ（P<0.10）and ileum TNF-α（P<0.05）,and upregulated the relative m RNA expression of TGF-β1 and IL-10 in jejunum（P<0.05）.（5）Maternal supra-nutritional Se supplementation upregulated the relative m RNA expression of ZO-1 in duodenum,Occludin,Claudin and ZO-1 in jejunum of offspring weaning piglets（P<0.05）.（6）Maternal supra-nutritional Se supplementation increased SEPHS2 relative protein expression of duodenum（P<0.05）,ileum（P<0.05）and jejunum（P=0.117）,as well as the relative protein expression of SEPP1 in jejunum and ileum（P<0.05）,GPX1 in duodenum and jejunum（P<0.05）and TXNRD1 in duodenum（P<0.05）of offspring weaning piglets.It can be concluded that maternal supra-nutritional Se supplementation improves the plasma Se status,intestinal antioxidant status,selenoprotein expression,inflammatory factors and barrier function in the offspring weaning piglets.Part 4.Effects of selenomethione on selenoproteins synthesis and antioxidant function in porcine mammary epithelial cells.The porcine mammary epithelial cells（PMEC）were used as in vitro model.PMEC were treated with 0,0.5,1.0,2.0,and 4.0μM Se-Met for 24,48,and 24 h,respectively,for the analysis of cell viability using CCK-8 kit.After 48 h incubation with 0,0.5,1.0,2.0,and 4.0μM Se-Met,PMEC were collected for measuring the expression of selenoprotein transcriptome using real-time PCR,and the relative protein expression of SEPHS2,SEPP1,GPX1 and TXNRD1 via western blot,and the GPX and TRX activity using commercial kits.The results show that:（1）Cell viability were increased first and then decreased after24,48 and 72 h of Se-Met treatment with Se-Met concentration increased.Compare with control group,the cell viability were elevated for 0.5,1.0 and 2.0μM Se-Met group when PMEC were incubated for 24 h（P<0.05）.When the cells were treated with Se-Met for 48h,the viability of the cells in the 0.5 and 1.0μM Se-Met group was significantly higher than that in the control group（P<0.05）.At 72 h,there was no significant difference in cell viability between the treatment groups and the control group（P<0.05）,but the cell viability of the 0.5μM Se-Met group was significantly higher than that of the 4.0μM Se-Met group（P<0.05）.（2）With the increase of Se-Met concentration,the relative m RNA expression of GPX4,TXNRD2,SELX,SELM and SELV did not change,and the relative m RNA expression of TXNRD3,SEPN1 and SELO decreased first and then increased,and17 selenoprotein relative m RNA expression increased first and then decreased,and the highest expression was at 0.5μM,including SEPHS2,SEPP1,GPX1,GPX2,GPX3,GPX6,TXNRD1,SELK,SEPW1,DIO1,DIO2,DIO3,SEP15,SELS,SELH,SELI,and SELT.（3）With the increase of Se-Met concentration,the relative protein expressions of SEPHS2,SEPP1,GPX1 and TXNRD1 increased first and then decreased,and the expression was highest at 0.5μM.（4）With the increase of Se-Met concentration,the GPX and TRX activities of PMEC increased first and then decreased,and the activities reached the maximum at 0.5μM.In summary,the in vivo experiment revealed that maternal supranational Se（1.2 mg/kg）improved preweaning survival of piglets by improving milk composition and the maternal transfer of immunoglobulins,Se and antioxidant status to the offspring nursing piglets.Besides,maternal supranational Se improved plasma Se status,intestinal antioxidant status,selenoprotein expression,inflammatory factors and barrier function in offspring weaning piglets.The in vitro experiment revealed that Se-Met（0.5μM）promoted PMEC cell viability by increasing the selenoproteins biosynthesis and antioxidant functions of PMEC.