TABLE 6.

Overview of heat stress effects on the GI epithelium of chickens.

Class	Heat stress effect	Pros	Cons	References a
GI epithelium	Altered GI epithelium morphology (microarchitecture) and enterocyte lifecycle	—	Digestive and absorptive dysfunctions → ↓ performance	Lambert (2009), Song et al. (2014) , Vaure and Liu (2014), Wang et al. (2015), Wideman (2016) , Dokladny et al. (2016) , Alhenaky et al. (2017) , Awad et al. (2017), France and Turner (2017), Ma et al. (2018), Wassenaar and Zimmermann (2018), Ducatelle et al. (2018) , He et al. (2018a) , He et al. (2018b) , Epstein and Yanovich (2019), Nanto-Hara et al. (2020) , Ruff et al. (2020 ), Tabler et al. (2020) , Liu et al. (2020) , Liu et al. (2022)
	↑ paracellular permeability (↓ transepithelial electrical resistance and ↑ mucosa-to-serosa flux of markers) → “leaky gut”
	↓ GI epithelium integrity		LPS/endotoxins leakage →↑ pro-inflammatory cytokines → GI inflammation and ↓ GI barrier
			↓ liver health and functionalityEndotoxemia → systemic inflammation, multi-organ failure, and septic shock
			“Bacterial translocation” →↓ liver health and functionalitybacterial chondronecrosis with osteomyelitis

Upward arrow (↑), increase; downward arrow (↓), decrease; rightward arrow (→), consequence/degeneration.

^aInclude studies on non-avian species that have exhibited comparable heat stress effects and responses to those observed in chickens. Studies with the focus on chickens or poultry are highlighted in bold.