日本畜産学会大会

High ambient temperature (HT) is a big challenge for the poultry industry under the growing global warming scenario as air-conditioning is not a feasible means to minimize HT in poultry farms. Novel nutritional candidates are needed to develop thermotolerance in chickens under HT. We have found that plasma citrulline (Cit) concentrations declined in heat-exposed chicks (Chowdhury et al., 2014). We have further found that oral administration of L-Cit caused to afford thermotolerance in chicks (Chowdhury et al., 2017) and broilers (Chowdhury et al., 2021). Plasma 3,5,3ˊ-triiodothyronine (T3), which initially increased due to heat stress, was reduced by oral administration of L-Cit. Oral administration of L-Cit caused activation of the urea cycle, and TCA cycle metabolism and reduced the activity in fatty acid metabolism in chick liver. HT exposed broilers showed that there were increased brain concentrations of Cit in comparison with concentrations in broilers exposed to control thermoneutral temperature (CT), whereas brain ornithine (Orn) concentrations were decreased, and arginine (Arg) concentrations were not changed. Interestingly, oral administration of L-Cit increased brain concentration of Cit, Arg, and Orn under both CT and HT. Tryptophan and its metabolite, serotonin (5-HT) concentrations were lower in the brain under HT than under CT. HT did not change brain concentrations of tyrosine, but dopamine (DA, a metabolite of tyrosine) concentrations decreased, and methoxyhydroxyphenylglycol (a metabolite of DA) concentrations increased in comparison with CT. Oral administration of L-Cit decreased brain concentrations of both tryptophan and tyrosine under CT and HT without changing 5-HT; however, DA levels declined under HT. In conclusion, these results suggest that L-Cit can serve as a potential nutritional factor to change central and peripheral metabolism to reduce body temperature and confer thermotolerance in chickens under heat stress.