What could be the most effective approach for preparing the chickens to withstand future Heat Stress challenges during their life?


ESR blog

High ambient temperatures affect animal production and welfare in tropical and sub-tropical regions of the world (He et al., 2018). Global climate change is primarily caused by greenhouse gas (GHG). The livestock sector contributes 14.5% of global GHG emissions (Gerber et al., 2013). The effects of climate change such as heat stress affects livestock production and eventually causing diseases and reducing the production performance of farm animals (Friel et al., 2009). The poultry sector is also face with the impact of climatic change coupled with global warming (Chang et al. 2020; Sohail et al. 2012). Due to the variations of global climate (environmental temperatures, humidity, precipitation patterns, and raising atmospheric carbon dioxide level), the poultry industry is severely affected (Nawab et al. 2018). However, among these environmental stress factors, heat stress (HS) is one of the most important factor influencing poultry performances including reduced feed intake, which in turn, affects growth rate, body weight, meat quality, egg quality, egg production, semen quality, and fertility; which cause huge financial losses in the poultry sector (Nawab et al. 2018; Kumar et al. 2021; Goel 2021). The decrease in the  productive potential of birds exposed to HS may be attributed to the deviation of energy resources from production to adaptation pathway (Vandana et al. 2021).

High ambient temperature has a negative impact on the performance traits of poultry. Thus, the selection of birds for high performance has increased their susceptibility to HS (Kumar et al. 2021). According to a report by (He et al., 2018), in the US, an amount of $128-165 million is lost from the poultry industry annually due to HS effects.

Therefore, it is essential to mitigate the deleterious effects caused by HS in poultry. Several strategies have been explored to address the adverse effects of HS in poultry which include genetic marker selection to enhance thermo-tolerance and productivity of poultry birds in hot regions of the world (Nawab et al. 2018), in ovo administration of bioactive substances (Slawinska et al. 2020; Elnesr et al. 2019; Zhu et al. 2020; Goel et al. 2021), housing management (Kapetanov et al. 2015; Pawar et al. 2016), early heat conditioning (Kang et al. 2019), thermal manipulation (Ncho et al. 2021; Li et al. 2007; Goel et al. 2021; Zaboli et al. 2017) and feeding management (Lin et al. 2006; Goel 2021; Li et al. 2007).

In ovo supplementation of bioactive substances

One intervention strategy to ameliorate the adverse effects of HS is the in ovo administration of bioactive substances (Slawinska et al. 2019). Prebiotics such as galactooligosaccharide (GOS) (Slawinska et al. 2020; Tavaniello et al. 2020) have been reported to improve poultry birds thermotolerance to HS. The in ovo administartion of 3.5 mg GOS/egg on 12th embryonic day (ED) could mitigate the detrimental effect of heat stress on some meat quality traits. Concomitantly, several research have shown that some amino acids and vitamins delivered on 17.5 ED, 18 ED, 15 ED, in ovo respectively improved the chicks’ oxidative state, which led to improvements in incubation results, chick quality and production performances (Ncho et al. 2021; Sgavioli et al. 2019; Zhu et al. 2020; Araujo et al. 2019), and minerals (McGruder et al. 2011). In a different study, it is reported that in ovo injection of L-Leu on 7 ED promoted the recovery of antioxidative status in broiler chickens after exposure to HS (Han et al. 2018).

Genetic selection of poultry

There is variation between poultry breeds in their level of thermo-tolerance (Mashaly et al. 2004), making genetic modification a potential method to alleviate HS. Genetic selection is a process of selecting good quality birds to produce the next progeny. Various aspects such as growth and immunity have been used as a selective parameter. The major problem with meat-type chicken has been associated with deprived feed intake under HS (Awad et al. 2020). Continuous selection in the last few decades targeted rapid growth in broilers. However, they are comparably more affected under HS due to lower heat tolerance compared to slow-growing broilers (Deeb and Cahaner 2002). Egg production performances are the main criteria for rearing laying hens. HS adversely reduces egg production and quality (Barrett et al. 2019). However, birds’ genetic selection helps reduce the decline in egg production performance and egg quality in laying hens (Radwan 2020). Fine-mapping with quantitative trait loci (QTL) is also effective for the screening of high HS tolerant birds. Identification of QTL for important parameters such as body temperature and weight is the essential requirement for such studies. Previous studies suggested that QTL enables the selection of heat-tolerant birds for improved growth performances in chickens (Van Goor et al. 2015). In marker-assisted selective breeding of poultry birds, polymorphisms in HSP genes, dwarf gene, frizzle gene, and naked neck genes are some of the important thermo-tolerant genes that can be used to develop a breed with superior thermotolerance (Chen et al. 2013; Yu et al. 2008).

Dietary and Nutritional Strategies

Among environmental stresses, the most significant factor influencing feed intake and subsequently weight gain in broilers is the ambient temperature. Several authors have demonstrated that bird’s growth depression because of HS can be partially alleviated by increasing the calorie content of the diet (Wasti et al., 2020; Attia et al., 2017). While the metabolism process, fat produces less heat compared to protein and carbohydrates, resulting in lower body temperature in birds. Fats and oil not only improve the energy density of other feed components but also slow down the food passage rate resulting into increased nutrient utilization (Attia et al., 2018). Dietary supplementation with up to 5% fats or oils helps to minimize heat generation due to their higher energy content and lower heat increase compared to carbs and proteins. In heat-stressed laying hens, increasing fat in the diet by 5% was found to increase feed intake by 17% (Daghir, 2008). Similarly, a significant increase in broiler performance was seen when the 5% fat diet was given (Ghazalah et al., 2008). In addition, broiler performance, meat lipids, and physiological and immunological features were all reportedly improved by increasing the oil supplementation in diets with greater protein concentrations (Attia et al., 2017). Care should be taken when choosing fats or oils because certain of them, such as soybean oil, canola oil, walnuts, flaxseed oil, and fish oil, have greater quantities of polyunsaturated fatty acids and should be avoided or be used at minimal levels in the diet.

Besides energy, the balance of amino acids in the diet must be taken into account during HS. If the energy level of the diet is increased, the other nutrients must be increased proportionally. Lower crude protein (CP) diets supplemented with limiting amino acids (mostly methionine and lysine) perform better than high CP diets during HS. Additionally, other studies found that lower CP diets resulted with lower FI (Awad et al., 2017, 2018). In addition to a low CP diet, several studies examined the effects of a high CP diet. During HS, High CP diets led to either an increase or a decrease in BWG and a reduction in FCR (Cheng et al., 1999; Faria Filho et al. (2005). However, some studies (Laudadio et al., 2012; Soares et al., 2020) found no difference between high and conventional CP diets, and the higher expense of high CP diets could result in negative economic effects (Cardoso et al., 2022).

Vitamins are undeniably significant components of poultry diets due to their anti-stress properties and decreased synthesis in HS. Vitamins A, E, and C supplements have gotten a lot of scientific attention as an antioxidant in chickens under HS conditions, along with other vitamins. All of them are efficient in slowing down the lipid peroxidation process by removing free radical forms under high heat in cell and subcellular organ membranes (Khattak et al., 2012).

Feeding Strategies

The strategy of withdrawing the feed before six hours of peak temperature time has been found promising as the passage rate allows feed to remain in the gut for up to six hours. Withholding food for at least 6 hours under HS reduced the broilers’ body temperatures, mortality, and heterophil-to-lymphocyte ratio, reducing the harmful consequences of HS (Yalçin et al., 2001, Lozano et al., 2006). Another strategy of dual feeding has been practiced in broilers by giving the birds a protein-rich portion of diet during the cooler part of the day and an energy-rich portion of diet during the warmer phase of the day (Teyssier et al., 2022). While a dual-feeding approach might be feasible in tropical areas and less-intensive production systems. Iyasere et al. (2021) estimated that it is unsuitable for most commercial production operations due to cost and logistical constraints. The most crucial component for broiler nutrition is water, which is also crucial for thermoregulation in hot environments. During HS, wet mash feeding is also suggested since the wet feed promotes micronutrient absorption by boosting total dry matter intake. Awojobi et al. (2009) and Dei and Bumbie (2011) found increased BWG in wet-fed birds raised in tropical settings (addition of 1 to 2 parts water to 1 part dry diet).

Housing Management

The proper design of the poultry shed might contribute to decrease HS by keeping optimal conditions within the shed. The shed’s roof that is between 10 and 12 meters high, which serves to lessen the intensity of direct solar radiation (Bhadauria et al. 2016). Other strategies to reduce radiation penetration, both direct and indirect, include insulating the roof and building the roof with an overhang (Oloyo and Ojerinde 2019). Overcrowding makes it harder for birds to lose heat and promotes disease transmission. Therefore, it is essential to provide enough floor space during heat waves. When birds are under HS, it might be beneficial to reduce overcrowding, so they have appropriate access to food and water (Kapetanov et al. 2015). With technological advancements, there has recently been an upsurge in the utilization of a closed house system for more intensive farming systems (NaRanong, 2007). However, such houses are expensive to build and operate in developing nations (Glatz and Pym, 2013).


The gradual increase of temperatures, and global warming coinciding with the expansion of the poultry industry in the tropical and subtropical regions makes it important to provide novel intervention strategies to mitigate the effects of stress. The effects of HS cause gut dysbiosis subsequently weakening the immune system of broiler chickens and making them more prone to pathogen infection. This also leads to poor production performance, mortality, and eventually leading to financial losses. Up to date, numerous strategies have been practiced, and new approaches are being tested to combat the adverse effects of HS on poultry production. Most of the approaches include in ovo administration of bioactive substances, genetic selection, dietary and feeding strategies and housing management that have proven beneficial to mitigate the detrimental effects of HS and provide aid to birds to maintain their growth. We created a poll and asked a question entitled: What could be the most effective approach for preparing the chickens to withstand future HS challenges during their life? This question with four possible answers was shared on the MonoGutHealth LinkedIn page for people to vote. After the polls, the results demonstrated that 42% of the people who voted shared that good house management is the most effective approach to mitigate HS in poultry, whereas 37% thought that genetic selection could be a potential strategy for this problem. Furthermore, in the case of in ovo supplementation of bioactive substances, only 12% suggested that it could ameliorate the adverse effects of HS in chickens, and 0% voted for specific diets for birds. In total, there were 19 votes.

In a nutshell, from the result of the votes, do you think that environment and housing management is the most effective approach for preparing chickens to withstand future heat stress challenges?

Figure 1. Different approaches to alleviate the deleterious effects of heat stress in poultry


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