Response of laying hens to L-arginine,L-citrulline and guanidinoacetic acid supplementation in reduced protein diet

A study was conducted with Hy-Line Brown laying hens to examine the effects of reduced protein diet,deficiency of arginine(Arg),and addition of crystalline Arg,citrulline(Cit)and guanidinoacetic acid(GAA)as substitutes for Arg.Hen performance,egg quality,serum uric acid,liver and reproductive organ weights,and energy and protein digestibility were measured using a completely randomized design with 5 treatments.Treatments were a standard diet(17%protein diet;SP),a reduced diet(13%protein diet deficient in Arg;RP)and RP with added Arg(0.35%,RP-Arg),GAA(0.46%equivalent to 0.35%Arg,RP-GAA)or Cit(0.35%,RP-Cit)to the level of SP.It was hypothesized that performance would decrease with Arg deficient RP diet and the addition of GAA or Cit in RP would allow birds to perform similar or greater than Arg-added RP treatment.The experiment was conducted from 20 to 39 wk of age but the treatment effect was seen only after 29 wk of age.The birds offered RP had reduced egg and albumin weights(P<0.01),lower yolk color score(P<0.01),lower protein intake and excretion(P<0.01)than those offered SP.When Arg or Cit were added to RP to make them equivalent to SP,feed intake(FI)and egg production were not different than those of RP(P>0.05).The birds offered RP-GAA decreased FI and egg production(P<0.01)compared to those offered RP.The addition ofArg,Cit or GAA to the RP had no effect on egg quality parameters,protein and energy digestibilities(P>0.05).However,birds offered the RP-Cit diet tended to have higher Haugh unit(P=0.095)and lower shell breaking strength(P=0.088)compared to all other treatments while those offered RP-GAA had higher energy digestibility(P<0.05)than all other groups but RP.The limited performance response of hens fed RP with added Arg,GAA,or Cit may be due to deficiency of some other nutrients in RP such as phenylalanine,potassium or non-essential amino acids and other components of soybean meal in the diet.

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.