Effects of in ovofeeding of L-leucine on amino acids metabolism and heat-shock protein-70, and -90 mRNA expression in heat-exposed chicks

Abstract

Recently, we found that in ovo feeding of L-leucine (L-Leu) stimulated the metabolism of lipids and afforded thermotolerance in male Chunky broiler chicks. In this study, we investigated the effects of feeding L-Leu in ovo on the metabolism of amino acids and on the cellular stress response mainly in the central and peripheral tissues in neonatal male broiler chicks and partly in embryonic tissues. Chicks (9 d old) were exposed to high ambient temperature (HT: 35 ± 1°C) or control thermoneutral temperature (CT: 28 ± 1°C) for 180min. The ambient temperatures were based on our recent reports and the recommendation of the Chunky broiler manual in which 28°C has been suggested as a normal ambient temperature for 5 to 9-d-old broiler chicks. In ovo feeding of L-Leu caused a significant (P < 0.05) decline in diencephalic arginine concentrations but it increased the diencephalic and plasma lysine concentrations when compared with the control chicks under HT. Notably, in ovo feeding of L-Leu significantly (P < 0.05) attenuated the increment of hepatic arginine compared with the control chicks under HT. Interestingly, in ovo feeding of L-Leu significantly (P < 0.05) attenuated the diencephalic gene expression of heat-shock protein (HSP) -70 and -90 in heat-exposed chicks. The gene expressions of mammalian target of rapamycin (mTOR) and its downstream genes (ribosomal protein S6 kinase (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1)) in the central and peripheral tissues were not influenced in the chicks under heat stress. We found that the gene expressions of mTOR, S6K1, and 4E-BP1 were significantly (P < 0.05) stimulated only in the embryonic breast muscle, and not in the other embryonic tissues, by in ovo feeding of L-Leu. In conclusion, in ovo feeding of L-Leu caused a change in the metabolism of amino acids in response to heat stress in broiler chicks. Attenuated gene expressions of HSP-70 and -90 under heat stress further suggests that in ovo feeding of L-Leu may afford thermotolerance in broilers.