Dietary protein levels and amino acid supplementation patterns alter the composition and functions of colonic microbiota in pigs

Different dietary nitrogen(N) patterns may have different effects on gut microbiota.To investigate the effects of different crude protein(CP) levels or essential amino acids(EAA) supplementation patterns on the structure and functions of colonic microbiota,42 barrows(25±0.39 kg) were randomly assigned to 7 dietary treatments including:diet 1,a high CP diet with balanced 10 EAA;diet 2,a medium CP diet with approximately 2% decreased CP level from diet 1 and balanced 10 EAA;diets 3,4,5,6 and 7,low CP diets with 4% decreased CP level from diet 1.Specifically,diet 3 was only balanced for Lys,Met,Thr and Trp;diets 4,5 and 6 were further supplemented with IIe,Val and IIe+Val on the basis of diet 3,respectively;and diet 7 was balanced for 10 EAA.Results over a 110-d trial showed that reducing the CP level by 2% or4% dramatically decreased N intake and excretion(P <0.05) in the presence of balanced 10 EAA,which was not observed when altering the EAA supplementation patterns in low CP diet(-4%).With balanced10 EAA,2% reduction in dietary CP significantly reduced Firmicutes-to-Bacteroidetes(F:B) ratio and significantly elevated the abundance of Prevotellaceae NK3 B31(P <0.05);whereas 4% reduction evidently increased the abundances of Proteobacteria,Succinivibrio and Lachnospiraceae XPB1014(P <0.05).Among the 5 low CP diets(-4%),supplementation with Ile,or Val+Ile,or balanced 10 EAA increased F:B ratio and the abundance of Proteobacteria.In addition,the predicted functions revealed that different CP levels and EAA balanced patterns dramatically altered the mRNA expression profiles of N-metabolizing genes,the "N and energy metabolism" pathways or the metabolism of some small substances,such as amino acids(AA) and vitamins.Our findings suggested that reducing the dietary CP levels by 2% to 4% with balancing 10 EAA,or only further supplementation with Ile or Val+Ile to a low protein diet(-4%) reduced the N contents entering the hindgut to various degrees,altered the abundances of N-metabolizing bacteria,and improved the abilities of N utilization.

Dietary guanidinoacetic acid supplementation improves water holding capacity and lowers free amino acid concentration of fresh meat in finishing pigs fed with various dietary protein levels

The current study was carried out to detect the effect of dietary guanidinoacetic acid(GAA)supplementation on carcass characteristics and meat quality in finishing pigs fed different dietary crude protein(CP)levels.Sixty-four barrows with an initial body weight of 73.05±2.34 kg were randomly allocated into 1 of 4 dietary treatments in a 2(100%vs.125%NRC CP level)×2(0 vs.300 mg/kg GAA)factorial arrangement(n=7).The feeding trial lasted for 49 d.GAA supplementation significantly reduced drip loss(P=0.01),free water distribution(T23peak area ratio)(P=0.05)and the concentrations of free alanine,threonine,methionine and isoleucine(P<0.05);but increased total glycine content(P=0.03)in the longissimus dorsi muscle of finishing pigs regardless of the dietary CP levels.Furthermore,primary myogenic cell differentiation system was employed to investigate the influence of inclusion of GAA on free amino acid concentrations in myotubes(n=4)and validate the finding in the animal feeding trial.We found that GAA inclusion in culture medium also decreased intracellular concentrations of free alanine,threonine,methionine,isoleucine,valine and proline in differentiated primary myogenic cells in vitro(P<0.05).Meanwhile,relative to diets with 100%NRC CP level,the intake of diets with 125%NRC CP level improved sarcoplasmic protein solubility,increased the contents of carnosine and total free amino acids as well as flavor amino acids in the longissimus dorsi muscle and decreased backfat thickness at the 6-7th ribs in pigs(P<0.05).In addition,we observed that the impact of dietary GAA supplementation on the last rib fat thickness,shear force,and free lysine content in the longissimus dorsi muscle was dependent on dietary CP levels(P<0.05).Collectively,dietary GAA supplementation can reduce drip loss,decrease the concentrations of free amino acids and flavor amino acids of fresh meat independent of dietary CP levels.