Mitigation strategies to ameliorate acute and chronic heat stress utilizing supplemental methionine or embryonic thermal conditioning in chickens

Abstract

Experiments were conducted exploring potential strategies to mitigate the negative effects of heat stress in chickens. In the first experiment, broilers were placed in environments which were heat treated (HT), thermoneutral (TN), or thermo-neutral coupled with pair-feeding (TN-PF). Birds were fed diets containing either DL-methionine (DLM) or 2-hydroxy-4-methylthiobutanoic acid (HMTBA) formulated to adequate or super-adequate levels of digestible sulfur amino acids (DSAA). Reduced (GSH), oxidized (GSSG), and total (TGSH) glutathione as well glutathione peroxidase (GPx) activity were measured to assess antioxidant capacity. Thiobarbituric acid reactive substances (TBARS) were measured to assess lipid peroxidation. Several blood variables were also measured. Responses were measured at 6 hours (acute) and 6 days (chronic). Growth over 6 days was impaired by HT (P < 0.01). Blood variables were altered during the acute phase. Birds fed DLM during the acute phase exhibited lower TBARS concentrations than those fed HMTBA (P = 0.02). Concentrations of GSSG were lower (P < 0.01) in birds receiving super-adequate DSAA than those receiving adequate DSAA in the acute phase. During the chronic phase, GSH and TGSH concentrations were higher (P = 0.02) in the HT group compared to the TN group. There were no effects on GPx activity. During the second experiment, broiler x Fayoumi crosses were incubated at a normal incubation temperature (NI; 37.8°C) or elevated incubation temperature (EI; 39.5°C) from embryonic day-12 to-4. Birds were then placed in TN or cyclical HT from 22 to 28 days of age. Growth performance and feed dry matter digestibility were assessed from 21 to 28 days of age. An interaction occurred where birds in the EI group in HT environments had higher xi digestibility than those birds in the NI group held at TN temperatures. The third experiment followed the same procedures from the second experiment, except all were incubated normally, then divided into groups in which birds had parents that were incubated normally (PN) or parents incubated at elevated temperatures (PE) from the previous experiment. Heat treatment during the third experiment increased BWG. In summary, neither methionine supplementation nor embryonic thermal conditioning improved growth performance during heat stress. performance, but generally did not affect lipid peroxidation or antioxidant status. Results indicated that source of methionine and concentration of DSAA did not consistently impact lipid peroxidation, antioxidant activity, or performance.

Histopathological Alterations of Ceca in Broiler Chickens (Gallus gallus) Exposed to Chronic Heat Stress.

“…HS has generally been found to be detrimental to small intestine's morphology in broiler chickens (Al-Fataftah and Abdelqader, 2014;Yi et al, 2016). The underlying mechanisms involve hypothalamic-pituitary-adrenal (HPA) axis activation, ischemia, oxidative stress, or perturbation of intestinal microbiota (Bolek, 2013;Song et al, 2014;Yi et al, 2016). The activated HPA axis subsequently elevates corticosterone level which in turn undermines immunity (Mishra and Jha, 2019).…”