A review of heat stress in chickens. Part I: Insights into physiology and gut health

Abstract

Heat stress (HS) compromises the yield and quality of poultry products and endangers the sustainability of the poultry industry. Despite being homeothermic, chickens, especially fast-growing broiler lines, are particularly sensitive to HS due to the phylogenetic absence of sweat glands, along with the artificial selection-caused increase in metabolic rates and limited development of cardiovascular and respiratory systems. Clinical signs and consequences of HS are multifaceted and include alterations in behavior (e.g., lethargy, decreased feed intake, and panting), metabolism (e.g., catabolic state, fat accumulation, and reduced skeletal muscle accretion), general homeostasis (e.g., alkalosis, hormonal imbalance, immunodeficiency, inflammation, and oxidative stress), and gastrointestinal tract function (e.g., digestive and absorptive disorders, enteritis, paracellular barrier failure, and dysbiosis). Poultry scientists and companies have made great efforts to develop effective solutions to counteract the detrimental effects of HS on health and performance of chickens. Feeding and nutrition have been shown to play a key role in combating HS in chicken husbandry. Nutritional strategies that enhance protein and energy utilization as well as dietary interventions intended to restore intestinal eubiosis are of increasing interest because of the marked effects of HS on feed intake, nutrient metabolism, and gut health. Hence, the present review series, divided into Part I and Part II, seeks to synthesize information on the effects of HS on physiology, gut health, and performance of chickens, with emphasis on potential solutions adopted in broiler chicken nutrition to alleviate these effects. Part I provides introductory knowledge on HS physiology to make good use of the nutritional themes covered by Part II.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

“…Lower expression and activity of digestive enzymes, including trypsin, chymotrypsin, lipase, amylase, and maltase, have been observed in broilers reared under high temperatures ( Hai et al, 2000 ; Song et al, 2018 ; Al-Zghoul et al, 2019 ). As described in Part I, oxidative stress induced by HS aggravates intestinal barrier disorders ( Brugaletta et al, 2022 ), and hyperthermia has been associated with a reduction in upper gastrointestinal tract blood flow that can induce degradation of the intestinal mucosa ( Song et al, 2014 ; Chegini et al, 2018 ). Following hot temperature exposure, the absorptive surface area of the small intestine is decreased due to a reduction in villi height, crypt depth ( Song et al, 2018 ; He et al, 2019 ), and relative jejunal weight ( Garriga et al, 2006 ).…”

“…When the environmental temperature rises above the thermoneutral zone, birds typically reduce their physical activity and feed intake (FI) to limit heat production (HP), as well as increase their panting and water consumption to favor heat loss by evaporation ( Renaudeau et al, 2012 ). Indeed, elevated temperatues trigger important physiologic and metabolic changes as described in Part I of this review ( Brugaletta et al, 2022 ), and chronic HS exposure results in significant losses in bird performance, negatively affects welfare, challenges food safety, and reduces the overall economic efficiency of poultry production ( Lara and Rostagno, 2013 ; Pawar et al, 2016 ). Consequently, HS has been estimated to cause annual economic losses of $128 to $165 million for the United States poultry industry ( St-Pierre et al, 2003 ), but these figures probably underestimate current and future losses due to the growth of the poultry industry over the last decade and the worsening of climate change predictions.…”

Metabolic and microbiota response to arginine supplementation and cyclic heat stress in broiler chickens

“…This therefore confirms that feeding diets high in arginine improves the performance of broilers under TN conditions. On the other hand, cyclic exposure to high environmental temperatures considerably impaired growth performance, reducing FI and BW gain, and increased body temperature and mortality, thereby causing some of the adverse effects typically observed in heat-stressed chickens (Brugaletta et al, 2022;Teyssier et al, 2022). Arginine supplementation, however, did not alleviate the deterioration in performance or prevent environmentally induced hyperthermia, as the birds responded similarly to the thermal stress irrespective of the diet they were fed on.…”

“…Rising environmental temperatures have a great impact on the sustainability of chicken meat production, affecting the performance and heath of birds (Renaudeau et al, 2012;Rostagno, 2020) and deteriorating product quality (Song and King, 2015;Wang et al, 2017;Zaboli et al, 2019). The risk of suffering from heat stress (HS) and its multifaceted and serious physiological consequences is extremely high for broilers, especially for fast-growing lines (Brugaletta et al, 2022). Looking for strategies intended to prevent or mitigate the detrimental effects of HS is therefore imperative and has become a major research topic in poultry science.…”

Blood Profile and Carcass Production of Broiler Chickens Given Nucleotides and Turmeric Extract in Feed

“…Furthermore, the salvage pathway, which harvests nucleobases from blood and diet, could support their demands (Gopi et al, 2020). Heat stress results in insufficient de novo synthesis of nucleotide, change chicken behavior and impair chicken performance (Brugaletta et al, 2022). Therefore, nucleotides are often added to animals' diets in the form of yeast extracts (Mohamed et al, 2020).…”