Effects Of Folic Acid On Ruminal Fermentation And Hepatic Protein Metabolism In Dairy Calves

This study evaluated the effects of folic acid(FA)supplementation on growth performance,ruminal fermentation,nutrient digestibility and hepatic protein metabolism in post-weaned dairy calves.Sixteen Chinese Holstein male dairy calves at 60 days of age and 88 ± 2.1 kg of body weight(BW)were assigned to four groups in a randomized block design.The treatments were:control,low FA(LFA),medium FA(MFA)and high FA(HFA)with 0,0.1,0.2 and 0.3 mg FA per kg BW per day,respectively.Dry matter intake linearly(P<0.05)decreased with increasing FA supplementation.Average daily gain(ADG)linearly(P<0.05)increased.Feed conversion ratio linearly(P<0.05)decreased.Digestibility of dry matter,organic matter,ether extract,acid detergent fibre and neutral detergent fibre linearly(P<0.05)increased.Digestibility of crude protein linearly(P<0.05)increased.The excretion of fecal nitrogen and urinary nitrogen linearly(P<0.05)decreased,whereas,digestible nitrogen,nitrogen retained as well as ratios of nitrogen retained to nitrogen intake and nitrogen retained to digestible nitrogen linearly(P<0.05)increased with increasing FA supplementation.Ruminal pH linearly(P<0.05)decreased with increasing FA supplementation.Total volatile fatty(VFA)acids concentration linearly(P<0.05)increased.Ammonia N content linearly(P<0.05)decreased.Activities of carboxymethyl cellulose,cellobiase,xylanase,pectinase and a-amylase linearly(P<0.05)increased.Activity of protease linearly(P<0.05)increased.Abundance of R.albus,R.flavefaciens,F.succinogenes,B.fibrisolvens and P.ruminicola linearly(P<0.05)increased,and was higher for MFA than for control.The R.amylophilus abundance was unaffected by FA supplementation.The excretion of uric acid was unaltered,whereas,allantoin and total PD linely(P<0.05)increased.Serum glucose concentration was similar among treatments,whereas,total protein and album concentration linearly(P<0.05)increased.Serum urean nitrogen and FA concentration linearly(P<0.05)increased,whereas,homocysteine concentration linearly(P<0.05)decreased.Serum concentrations of growth hormone releasing hormone(GHRH),growth hormone(GH)and insulin-like growth factor-1(IGF-1)linearly(P<0.05)increased with increasing FA supplementation.Somatostatin(SS)concentration linearly(P<0.05)decreased.The relative expressions of GH,GHR,IGF-1 and IGF-1R in the liver of calves linearly(P<0.05)increased,.The expression of SS linearly(P<0.05)decreased.The relative expressions of 5,10-methylenetetrahydrofolate reductase(MTHFR),methionine synthase reductase(MTRR)and methionine synthase(MS)linearly(P<0.05)increased.The relative expressions of liver kinase B 1(LKB1),Adenosine monophosphate activated protein kinase(AMPK)and tuberous sclerosis complex 2(TSC2)linearly(P<0.05)increased.The expressions of phosphoinositide 3-kinase(PIK3),3-phosphoinositide dependent kinase-1(PDK),3-phosphoinositide dependent kinase-2(PDK2),protein kinase-B2(AKT2),ribosomal protein S6 kinase(P70S6K),eukaryotic translation initiation factor 4E(4EBP1),eukaryotic initiation factor 4E(eIF4E)and mammalian target of rapamycin(mTOR)linearly(P<0.05)increased,whereas,Uncoordinated 51-like kinase-1(ULK1)linearly(P<0.05)decreased.The results indicated that ADG,ruminal total VFA concentration,nutrient digestibility and urinary PD excretion increased due to an increased ruminal microbial abundance and enzyme activity with FA supplementation.Hepatic protein synthesis was promoted due to an upregulated genes expression of PI3K/AKT/mTOR signaling pathway with FA supplementation.The optimum supplementary dose of FA was 0.2 mg per kg BW per day for calves.