Age-related oxidative stress and antioxidant capacity in heat-stressed broilers

We aimed to evaluate the effects of acute heat stress (HS) and age on the redox state in broilers aged 21 and 42 days. We evaluated the expression of genes related to antioxidant capacity, the production of hydrogen peroxide (H2O2), and the activity of antioxidant enzymes in the liver, as well as oxidative stress markers in the liver and plasma. The experiment had a completely randomized factorial design with two thermal environments (thermoneutral and HS, 38°C for 24 h) and two ages (21 and 42 days). Twenty-one-day-old animals exposed to HS showed the highest thioredoxin reductase 1 (TrxR1) (P<0.0001) and glutathione synthetase (GSS) (P<0.0001) gene expression levels. Age influenced the expression of the thioredoxin (Trx) (P=0.0090), superoxide dismutase (SOD) (P=0.0194), glutathione reductase (GSR) (P<0.0001) and glutathione peroxidase 7 (GPx7) (P<0.0001) genes; we observed greater expression in birds at 21 days than at 42 days. Forty-two-day-old HS birds showed the highest H2O2 production (222.31 pmol dichlorofluorescein produced/min×mg mitochondrial protein). We also verified the effects of age and environment on the liver content of Glutathione (GSH) (P<0.0001 and P=0.0039, respectively) and catalase (CAT) enzyme activity (P=0.0007 and P=0.0004, respectively). Higher GSH content and lower CAT activity were observed in animals from the thermoneutral environment compared with the HS environment and in animals at 21 days compared with 42 days. Broilers at 42 days of age had higher plasma creatinine content (0.05 v. 0.01 mg/dl) and higher aspartate aminotransferase activity (546.50 v. 230.67 U/l) than chickens at 21 days of age. Our results suggest that under HS conditions, in which there is higher H2O2 production, 21-day-old broilers have greater antioxidant capacity than 42-day-old animals.