Effects Of Protein And Folic Acid On Growth Performance And Protein Metabolism Gene Expression In Dairy Calves

The objective of this study was to determine the effects of protein and folic acid on growth performance and protein metabolism gene expression in dairy calves.Sixteen Chinese Holstein dairy calves with 9 mouths of age and 286.8 ± 2.3 kg of body weight were assigned to one of four groups in a randomized experimental design with a 2(normal protein [NPD,130.1 g CP/kg] or high protein [HPD,150.2 g CP/kg] diets)× 2(3.6 mg FA per kg diet DM or 3.6 mg FA as rumen-protected folic acid [RPFA]per kg diet DM)factorial arrangement.The results showed that:(1)For growth performance and digestion metabolism,average daily gain(ADG),nutrient digestibility,nitrogen retained(RN)and RN/digestible nitrogen(DN)was higher in calves fed HPD than NPD,while feed conversion ratio(FCR)followed the opposite trend(P<0.05);For blood metabolites,the concentrations of glucose,albumin,total protein,urea,triglyceride,folates and leptin in serum was higher in calves fed HPD than NPD,while the concentrations of non-esterified fatty acid(NEFA),acetoacetate and Homocysteine(Hcy)in serum followed the opposite trend(P<0.05);For rumen metabolism,total volatile fatty,acetate(A)/propionate(P),the concentration of ammonia nitrogen in rumen fluid,rumen microbial enzyme activity,ruminal bacteria populations and urinary excretion of purine derivatives was higher in calves fed HPD than NPD(P<0.05).(2)For growth performance and digestion metabolism,dry matter intake(DMI),ADG and RN was higher in calves received RPFA than FA(P<0.05),while urinary nitrogen followed the opposite trend(P<0.05).For blood metabolites,the concentrations of glucose,albumin,total protein,folates and leptin in serum was higher in calves received RPFA than FA(P<0.05),while the concentrations of urea,NEFA,triglyceride,acetoacetate,?-hydroxybutyrate and Hcy in serum followed the opposite trend(P<0.05).For rumen metabolism,ruminal p H and molar proportion of propionate was higher in calves received RPFA than FA(P<0.05),while A/P and the concentration of ammonia nitrogen in rumen fluid was lower(P<0.05).(3)The concentrations of growth hormone,growth hormone releasing hormone,insulin-like growth factor-1 and insulin in serum and m RNA relative expressions of these hormones and the receptors on liver and muscle was increased by both HPD and RPFA supplementation(P<0.05).Furthermore,m RNA relative expressions of amino acid activate mammalian target of rapamycin complex 1(m TORC1)signaling,phosphoinositide 3-kinase/protein kinase(PI3K/AKT)-m TORC1 signaling and AMP-activated protein kinase(AMPK)-m TORC1 signaling followed the same trend on liver and muscle(P<0.05).Hepatic m RNA relative expression of5,10-methylenetetrahy-drofolate reductase(MTHFR),methionine synthase reductase(MTRR)and methionine synthase(MS)and intramuscular m RNA relative expression of MTHFR and MS was increased by both HPD and RPFA supplementation(P<0.05).(4)The interaction effect between different protein level and FA administration mode was observed on ruminal molar proportion of acetate and propionate,serum concentration of insulin(P<0.05).The results indicated that the effects of RPFA supplementation were better than FA suggested by the growth performance,nitrigen utilization,hormone secretion and protein metabolism was improved by RPFA supplementation.The interaction effect between different protein level and FA administration mode was observed on hormone secretion and rumen fermentation.