Dietary L-citrulline supplementation modulates nitric oxide synthesis and antioxidant status of laying hens during summer season

Background:L-citrulline(L-Cit),a non-protein amino acid,has been implicated in several physiological functions including anti-inflammatory,anti-oxidative,and hypothermic roles,however,there is a paucity of information with regards to its potential in poultry production.Methods:This study was designed to investigate the effects of dietary L-Cit supplementation on the production performance,nitric oxide production,and antioxidant status of laying hens during summer period.Hy-Line Brown laying hens(n=288,34 weeks old)were allotted to four treatment,6 replicates of 12 chickens each.Dietary treatments of control(basal diets),0.25%,0.50%and 1.00%L-Cit supplementation were fed to chickens for eight(8)weeks.Production performance,free amino acid profiles,nitric oxide production,and antioxidant properties were measured.Blood samples were collected at the 4th and 8th weeks of the experiment.Results:Air temperature monitoring indicated an average daily minimum and maximum temperatures of 25.02°C and 31.01°C respectively.Dietary supplementation with L-Cit did not influence(P>0.05)the production performance,and rectal temperature of laying hens.Egg shape index was increased(P<0.05)with increasing levels of L-Cit.Serum-free content of arginine,citrulline,ornithine,tryptophan,histidine,GABA,and cystathionine were elevated,but taurine declined with L-Cit diets.Plasma nitric oxide(NOx)concentration was highest at 1%L-Cit.Likewise,nitric oxide synthase(NOS)activity for total NOS(tNOS)and inducible NOS(iNOS)were upregulated with increasing L-Cit levels,although,tNOS was not affected at the 4th week.Anti-oxidant enzymes including catalase and superoxide dismutase(SOD)were increased with L-Cit supplementation,however,SOD activity was unchanged at 4th week,while total anti-oxidant capacity increased at the 8th week.L-Cit supplementation attenuated the extent of lipid peroxidation,and also inhibited glutathione peroxidase activity.Conclusion:Dietary L-Cit supplementation modulated systemic arginine metabolism,nitric oxide synthesis,antioxidant defense system,and increased the egg shape index of laying hens during the summer season.1%L-Cit supplementation proved most effective in potentiating these effects and may be adopted for feed formulation strategies.