N-acetylcysteine improves the growth performance and intestinal function in the heat-stressed broilers

• Diet supplemented with 1 g/kg N-acetylcysteine (NAC) decreased the feed/gain and mortality rate of heat-stressed broilers.
• NAC improved intestinal morphology, absorptive function, and energy status of heat-stressed broilers.
• NAC mitigated intestinal oxidative stress and enhanced the resistance to heat stress in broilers.

This study was carried out to investigate the effects of N-acetylcysteine (NAC) on growth performance and intestinal function of heat-stressed broilers. A total of two hundred 1-d-old Cobb male chicks were allocated to 1 of 4 treatments, with 5 replicated pens per treatment and 10 birds per pen. The experiment consisted of 4 treatments in a 2 × 2 factorial arrangements with two diets (basal diet or 1 g/kg NAC diet) and two temperatures (thermoneutral or heat stress). From day 8–35 of age, broilers were raised at thermoneutral (26 ± 1 °C) or exposed to cyclic heat stress (36 ± 1 °C from 0800 to 1800 and 26 ± 1 °C from 1800 to 0800). The results showed that heat stress reduced ADFI, ADG, plasma concentrations of triiodothyronine (T3) and thyroxine (T4), intestinal villus height (VH), ratio of VH to crypt depth (CD), intestinal mucosal ATP level, adenylate energy charge (AEC), activities of alkaline phosphatase (AKP), antioxidative and digestive enzymes, and mRNA level for Bcl-2, whereas increased the feed/gain, mortality rate, plasma corticosterone level, intestinal CD, intestinal mucosal AMP and malondialdehyde (MDA) levels, and mRNA levels of heat shock protein (HSP70), caspase-3, AMP-activated protein kinase (AMPK), heme-oxigenase (HMOX), and xanthine oxidoreductase (XOR). Dietary supplementation with NAC decreased the feed/gain, mortality rate, plasma corticosterone level, MDA concentration and intestinal mucosal mRNA levels of HSP70, AMPK and HMOX, while elevated the ratio of VH to CD, ATP, catalase (CAT) and trypsine activity in the small intestine of heat-stressed broilers. Taken together, these results suggest that dietary supplementation of 1 g/kg NAC could improve growth performance and intestinal function of broilers exposed to heat stress.