Effect of N-acetyl-L-cysteine administration in drinking water of broilers exposed to heat stress on performances, intestinal integrity, and oxidative status

Abstract

Supplementing the diet of broiler with N-acetyl-L-cysteine (NAC) has been shown to support small intestinal integrity, and as a precursor of L-cysteine, it may also support antioxidant functions. As heat-stressed chickens suffer from intestinal disturbances caused by oxidative stress and at the same time increase water consumption, it was hypothesised that NAC supplemented via the drinking water could reinforce finisher broiler productivity under heat stress. Hence, three hundred 15-day-old male Ross 308 broilers were assigned to three treatments until 39 days of age: thermoneutral (TN), heat-stressed (HS), or HS + NAC. NAC was administered to the drinking water at 1000 mg/L starting on day 20. At 22 days, a chronic cyclic heat stress model was initiated in the HS and HS + NAC groups. On day 39, birds were euthanized and sampled for physiological measurements. Heat stress significantly decreased weight gain and feed intake from 22 to 39 days but did not affect feed efficiency. Rectal temperature and respiration rate significantly increased in heat-stressed broilers on days 23, 30, and 38. Also, ileal mucosal malondialdehyde (MDA) and plasma MDA levels were significantly higher in the HS group and the HS + NAC group, respectively, as compared to the TN group, whereas MDA levels in lung tissue were lower in both HS groups. Small intestinal villus height was significantly lower and serum FITC-d levels were significantly higher in the HS group compared to the TN group, without the effect of NAC supplementation. Furthermore, hepatic gene transcript of glutamate-cysteine ligase catalytic subunit was upregulated under heat stress conditions which may reflect higher glutathione synthesis, whereas in HS + NAC birds cystathionine-beta synthase-like (CBSL) mRNA level was dramatically reduced, indicating decreased transsulfuration activity. In conclusion, the administration of 1000 mg/L NAC in drinking water did not alleviate the reduced performances of heat-stressed finisher broilers. Nevertheless, it resulted in the downregulation of CBSL expression, suggesting a potential methionine-sparing effect.