| The present research was conducted to study the effects of folic acid supplemental levels on the growth performance, serum biochemical parameters and the mRNA expression of 5,10-Methylenetetrahydrofolate reductase(MTHFR), Folate Binding Proteins(FOLBP) and mammalian target of rapamycin(mTOR) in livers of weaned piglets. A total of one hundred and sixty pigs (80 of Landrace and 80 of Yorkshire),initially 7.33±0.67kg and 25 d of age, were randomly assigned to diets containing 5 levels of folic acid:basal diets supplemented with no folic acid (C),0.5mg/kg folic acid (FS0.5),2.5mg/kg folic acid (FS2.5),5mg/kg folic acid (FS5),or 10mg/kg folic acid (FS10) in groups of 8 pigs per pen, with 4 replicate pens per dietary treatment. The experimental diets were fed for 4 wk in 2 phases (phase 1,wk 1 and 2;phase 2, wk 3 and 4). The piglets were weighted and blood samples were collected from a subset (n=20;4 pigs/treatment) of the piglets on d 0,14, and 28.Livers, kidneys, hearts and muscles samples were collected from the blood-taken piglets on d 28 of the experiment. The serum routine indexes were determined by full automatic biochemical analysor, serum and tissue folate and serum insulin-like growth factor 1(IGF-1) concentrations were measured using radioimmunoassay, serum and tissue homocysteine, serum growth hormone (GH),insulin (INS) and cortisol concentrations were analyzed by chemiluminescence method, liver and muscle total protein, RNA and DNA levels were determined by Coomassie brilliant blue G-250,phenol extraction and strong salt, respectively. Real time-quantitative RT-PCR was applied to determine the mRNA expression of MTHFR, FOLBP and mTOR gene expression difference in livers. The results were shown as follows:1,Pigs fed basal diet supplemented with 2.5mg/kg folic acid grew faster (p<0.05)and consumed more feed (p<0.01)than groups of C,FS5,and FS10 during the last two weeks. Likewise, FS2.5 resulted in greater improvements in ADG (p<0.05)than C and FS10 during the entire period of experiment. FS5 and FS10 contributed no improvements of ADG and ADFI compared with C.Dietary treatment had no effect on F/G throughout the experiment.2,With increased folate supplemental levels, the serum folate concentrations obviously enhanced which showed highly significant positive correlation (p<0.01).Liver, kidney and heart folic acid concentrations significantly increased with the increased folate supplemental levels (p<0.05),but there were no significant differences between folate supplemental levels and muscle folate concentrations (p>0.05).Serum homocysteine concentrations showed highly significant negative correlation (p<0.01)with the dietary folate supplemental levels. Liver homocysteine concentration in FS2.5 was significantly lower (p<0.05).than C.Folate supplemental levels had no significant effects on kidney, heart and muscle homocysteine concentrations (p>0.05).3,Serum total protein (TP) and albumin (ALB) of FS2.5 were higher (p<0.05) than C at the end of the experiment. Serum urea nitrogen (SUN) in FS2.5 was significantly lower (p<0.01) than C on d 28 of postweaning. Serum alanine transaminase (ALT) of FS2.5 and FS5 were higher (p<0.05)than C at the end of the experiment. Serum globulin (GLOB), alkaline phosphatase (ALP), creatinine and aspartate transaminase (AST) concentrations were not affected by different folate supplemental levels.Pigs of FS2.5 showed greater concentrations of growth hormone (GH) (p<0.05)and insulin-like growth factor 1(IGF-1)(p<0.01)in serum than C and FS10 on d 28.Serum IGF-1 concentration in FS0.5 was significantly higher (p<0.05) than C and FS10.Serum cortisol in FS2.5 was significantly lower (p<0.05)than C on d 14 and d 28 of postweaning. There were no significant differences between folate supplemental levels and serum insulin concentrations (p>0.05).4,Liver DNA concentration in FS2.5 was higher (p<0.05)than C and FS10 and RNA was higher than FS10 (p<0.05).Muscle RNA/DNA in FS0.5 and FS2.5 (p<0.05)was also higher than C.Different folate supplemental levels had no effects on liver RNA/DNA and muscle RNA and DNA (p>0.05).Liver protein concentration and muscle RNA/protein in FS2.5 was significantly higher than C (p<0.05).Folate supplemental levels had no significant effects on liver RNA/protein and muscle protein concentrations (p>0.05).5,Real-time quantitative PCR analysis revealed that FS0.5,FS2.5,and FS5 had a greater abundance of the mRNA encoding MTHFR than C and FS10 (p<0.01).The mRNA expressions of FOLBP in FS0.5 and FS2.5 were up-regulated compared with pigs fed basal diet (p<0.05).The mRNA expression of mTOR in FS0.5 was highly significantly greater than C (p<0.01)and mTOR gene expression of FS 2.5 and FS5 was also greater than C (p<0.05).The results indicated that folate supplemental level of 2.5mg/kg in diet made up of corn, soybeans, soybean meal, fish meal and plasma protein significantly enhanced the growth performance of piglets and stimulated folate metabolism and liver protein synthesis and reduced the homocysteine concentrations. |
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