Effects of dietary N-acetylcysteine on rectal temperature, respiratory rate, growth performance and blood redox parameters in 22-to 42-day old broilers exposed to chronic heat stress

The present study investigated the effects of N-acetylcysteine (NAC) supplementation on rectal temperature, respiratory rate, growth performance and redox status in broilers, over a 21-day period at an elevated environmental temperature. A total of 270 one-day-old Arbor Acres broiler chickens were randomly allocated into three groups with five replicates of 18 broilers per replicate, viz. a thermoneutral group, which was reared at standard ambient temperature and fed a basal diet (CONT); and two heat-stressed groups, which were held at 32 +/- 1 degrees C from days 22 to 42 and fed a diet without NAC (HS) or with 0.1% NAC (HS+0.1% NAC), respectively. Rectal temperature (RT), respiratory rate (RR), growth performance and serum redox parameters were analysed on d 28, d 35 and d 42. HS treatment significantly impaired growth performance (P<0.01, P<0.05) and increased RT and RR (P<0.01, P<0.05) when compared to those of the CONT group over the entire experimental period. Moreover, serum total antioxidant capacity, activities of superoxide dismutase and glutathione peroxidase, ability to inhibit hydroxyl radical, sulfhydryl group, glutathione and Vitamin C and E levels, were significantly decreased (P<0.05, P<0.01) in the HS birds, as compared to those of the CONT group on d 28 and d 35. Serum malondialdehyde content, however, depicted an opposite trend simultaneously. NAC supplementation significantly reversed the adverse effects by significantly decreasing RR(P<0.01)and increasing weight gain, feed intake and partial antioxidant values on d 28 and d 35. In conclusion, addition of NAC in the diet limits effectively adverse effects of HS by decreased RR and improved performance and redox status, which indicate that NAC is potent in counteracting chronic heat stress.