Influence of Heat Stress on Intestinal Epithelial Barrier Function, Tight Junction Protein, and Immune and Reproductive Physiology

Table 1

Effects of heat stress on different body functions of animals.

S.No	Species	Body functions involved	Effects of heat stress	References
1	Calves	Immune function	Decreased ratio of circulating antibodies (IgG and IgM), reduced systemic humoral responses, increased expression of inflammatory factors, effect on lactation performance, and damage to the immune function which ultimately affect the health and growth performance of calves	[12, 36–39]
2	Chickens	Gut function	Reduced nutrient absorption, poor performance of gut wall integrity, increased disease susceptibility, and higher mortality in chickens	[40]
3	Birds	Tight junction permeability	Compromised TJ barrier and luminal contents enter into the blood circulation. Therefore, a leaky gut induces chronic systemic inflammation which reduces the disease-resistance capacity of birds and induces changes in tight junction protein expression	[41, 42]
4	Birds and other animals	Reproductive function	Decreased secretion of the gonadotrophin-releasing hormone (GnRH) in laying birds which brings infertility and also delays in the process of ovulation via reducing follicular size, estradiol concentrations, and expression of LH receptors. Also effects on the epigenetic modification of sperms which interferes with the active demethylation of DNA in the male pronucleus of fertilized eggs, thereby reducing the fertility of sperms	[25, 43, 44]
5	Mice	Ovarian function	Heat stress damaged the ovary microstructures, thereby reducing fertility	[45]
6	Livestock	Growth and performance	Under HS, animals often have listlessness, shortness of breath, decreased food intake reducing growth performance, poor meat quality, reproductive performance, and immunity function which lead to death in severe cases	[46]
7	Pig/swine	Intestinal peristalsis	Under HS, the gastric emptying time and the intensity of intestinal peristalsis of animals are prolonged and weakened, which reduces the mechanical digestive function, resulting in accumulation of chyme and inhibition of appetite	[47]
8	Livestock and poultry rats	Intestinal absorption function	Serious damage to the intestinal structure by significant reduction of the height of intestinal villi, increase in the depth of crypt, decrease in the value of V/C, intestinal villi rupture, edema, and shedding of epithelial cells at the top of villi. Congestion, edema, exfoliation, and thinning of intestinal wall	[48–51]