Potential Role of Amino Acids in the Adaptation of Chicks and Market-Age Broilers to Heat Stress

Abstract

Increased average air temperatures and more frequent and prolonged periods of high ambient temperature (HT) associated with global warming will increasingly affect worldwide poultry production. It is thus important to understand how HT impacts poultry physiology and to identify novel approaches to facilitate improved adaptation and thereby maximize poultry growth, health and welfare. Amino acids play a role in many physiological functions, including stress responses, and their relative demand and metabolism are altered tissue-specifically during exposure to HT. For instance, HT decreases plasma citrulline (Cit) in chicks and leucine (Leu) in the embryonic brain and liver. The physiological significance of these changes in amino acids may involve protection of the body from heat stress. Thus, numerous studies have focused on evaluating the effects of dietary administration of amino acids. It was found that oral l-Cit lowered body temperature and increased thermotolerance in layer chicks. When l-Leu was injected into fertile broiler eggs to examine the cause of reduction of Leu in embryos exposed to HT, in ovo feeding of l-Leu improved thermotolerance in broiler chicks. In ovo injection of l-Leu was also found to inhibit weight loss in market-age broilers exposed to chronic HT, giving rise to the possibility of developing a novel biotechnology aimed at minimizing the economic losses to poultry producers during summer heat stress. These findings and the significance of amino acid metabolism in chicks and market-age broilers under HT are summarized and discussed in this review.

The Microbiota-Gut-Brain Axis During Heat Stress in Chickens: A Review

“…Typically, the reduction in food intake is sustained during heat stress and is thought to be a compensatory mechanism to reduce heat production associated with nutrient metabolism, although heat stress is associated with changes in nutrient absorption, particularly amino acids and glucose. For this reason, a multitude of heat stress studies with chickens and other species have employed dietary strategies to mitigate nutrient-induced heat production, including formulating diets to vary in macronutrient composition ( Chowdhury et al, 2021 ). The GIT of chickens consumes about 7% of the energy derived from the diet, so reduced feeding, while offsetting some of the heat production in the animal, could also elicit a fast and dramatic response in the GIT, primarily jeopardizing gut integrity and mucosal immunity, which further compromises nutrient assimilation, triggers systemic inflammation, and impairs production ( Thompson and Applegate, 2006 ; Deng et al, 2012 ).…”

Functional role of branched chain amino acids in poultry: a review

“…(2015) injected about 1% leucine and isoleucine, which were equivalent to 453 mg leucine and 271 mg isoleucine in egg, in ovo beneath the air sac of eggs before incubation and reported that it accelerated the embryo growth and reduced the hatching time of chicks. In ovo feeding of L-leucine has been reported to improve thermotolerance and increase BWG of broilers during heat stress ( Chowdhury et al., 2020 ; Han et al., 2020 ; Table 2 ). Compared to isoleucine or valine, in ovo injection of 35 µmol leucine/500 µL of sterile water in the yolk sac of the embryo on d 7 significantly reduced the body temperature at hatching and improved chicks’ weight until 5 d of age by Han et al.…”

Protein and Amino Acid Metabolism in Poultry during and after Heat Stress: A Review

“…A study [74] attributed these effects to lower feed consumption, decreased consumption of AA, and therefore poor body weight gain and feed efficiency. According to a review [75], HS reduced AA levels in the birds including citrulline in chicks' plasma and leucine in the embryonic brain and liver. As a result, oral L-citrulline increased thermotolerance and decreased body temperature in layer chicks.…”