Effective Measures to Alleviate Heat Stress in Poultry

Effective Measures to Alleviate Heat Stress in Poultry

 Ajithakumar H. M^1*.  Paramesha S C², Shivanagouda Patil³, Shwetha H S⁴, Anandita Srivastava⁵ and Aparna Hebbar H ⁶.

^1,2,3,4,6 Assistant professor, Shri Baurao Deshapande Veterinary College, Athani. KVAFSU Bidar, Karnartaka 591230

⁵ Dr Anandita Srivastava, Assistant Professor, Bihar Veterinary College, Bihar Animal Sciences University, Patna. 800014

*Corresponding Author – Ajith.hudedh@gmail.com

Introduction

As a general term, stress is used to describe the sum of nonspecific or defence mechanisms of the body when it is confronted with abnormal or extreme demands. For poultry, it can be defined as the set of responses to external demands, which force flocks to adapt to a new or abnormal situation. The body temperature of the adult fowl is in the range of 41-42°C. The interaction of air temperature, humidity, radiant heat and air speed plays a major role in the creation of heat stress. In the case of poultry, the thermo-neutral zone is 18-21°C. When environmental temperature exceeds 35°C birds are likely to experience heat stress. The expression of heat stress in poultry production can be described as ‘acute’ or ‘chronic’. The chicks hyperventilate and increase their respiratory rate when the temperature reaches beyond the comfort zone, as they initially attempt to dissipate the heat through radiation, convection and conductance. Later they follow respiratory-evaporative mechanisms. The evaporative heat loss via panting is associated with loss of body water content, as well as through extensive cutaneous evaporation. To minimise production losses as well as maintain welfare there is a need to look for amelioration means to counter heat stress in birds. This article focuses on the scientific evidence available on the importance and impact of heat stress and measures to counter stress on birds.

Key Words – Heat Stress, Poultry, Genetic Selection, vitamins

Effect of heat stress

Birds with heat stress exhibit lower feed intake in order to reduce the thermogenic effect related to nutrient absorption and utilisation. Cumulative feed intake and weight gain is depressed in old broilers by 16-53 g (approximately) per bird for every 1°C increase in ambient temperature respectively. The growth rate decreases with an increase in ambient temperature above 25°C. As a result, performance may decrease due to decreased feed consumption, impaired metabolism, inefficient digestion and the genetic makeup of birds during heat stress. Further, heat stress affects the lymphoid organs (bursa, spleen and thymus), and white blood cells and results in an increased number of monocytes, heterophils and lymphocytes. It reduces the immune response of birds. Heat stress reduces the concentrations of IgM and IgG and suppresses the production of antibodies in young chickens. Heat stress generates free radicals like O₂– and HO which may harm cell membranes by induction of lipid peroxidation of polyunsaturated fatty acids in these cell membranes. Increased temperature up to 42°C increases panting and reduces the activity and spreading of wings in birds. When the temperature reaches lethal limits (up to 47°C), many birds are likely to die. Increased mortality during heat stress may occur because of inefficient cooling by evaporation leading to an accumulation of heat inside the body. The accumulated heat continuously increases body temperature and may lead to cardiac arrest or adrenal cortical insufficiency or ionic imbalance in the blood.

How do birds lose heat?

 Heat can be lost in a variety of ways. Three normal methods of heat loss are listed below. Birds modify their behaviour to stay in the ‘thermoneutral zone’.

Radiation: Heat will be lost from the body by radiation if the surrounding surfaces are below bird surface temperature. Conversely, hot walls and roofs may radiate heat to the bird surfaces.

Convection: Heat loss will occur from the natural rise of warm air from around a hot body. Providing moving air can assist convection, but only if the air moves fast enough to break down the boundary layer of still air that surrounds the body.

Conduction: Heat will transfer from one surface in contact with another surface, for example, if the birds are seated on litter that is cooler than their bodies. However, the litter immediately under the birds soon assumes a temperature close to that of the body. After a bird can no longer maintain its body heat balance by one of these three methods (upper critical temperature), it must use “evaporative heat loss”, or panting. Evaporative heat loss, whilst essential to the bird, does not contribute to heating the house.

Evaporation: This is very important at high temperatures as poultry do not sweat but depend on panting. This is only effective if the humidity is not too high. Hot, humid conditions are therefore much more stressful than hot dry conditions.

Strategies to Reduce Heat Stress in Poultry

Genetic Selection: Recent advances in genetics and biotechnology may enable modifications in chicken genes to help alleviate heat stress. Developing poultry lines with genes that mitigate heat stress is crucial for boosting production in high-producing chickens in hot areas, meeting the needs of the rising global population.

Genetic selection involves choosing high-quality birds to produce the next generation. Over the years, various parameters, such as growth and immunity, have been used to select the best birds for production. However, one of the main drawbacks of broilers is their low feed intake during high heat waves (Awad et al., 2020). Various genes associated with heat tolerance have been studied. One example is the dominant gene for the naked neck (Na), which is linked to a reduction in feather cover (Toth et al., 2021). While others, such as the sex-linked recessive gene for dwarfism, reduce body size and thereby lower metabolic heat output, the frizzle (F) gene causes the contour feathers to curve outward away from the body. Furthermore, it is reported that the F gene (as Ff) reduces the feather weight of broilers, in addition to the reduction caused by the Na gene (Deeb and Cahaner, 2002). The slow feathering (K) gene has been extensively used to ‘auto-sex’ strains and breed crosses, which affect increased heat loss during early growth. This may assist the bird in resisting heat stress (HS) (Tixier‐Boichard et al., 1989). Chickens with such genetic mutations are valued for their high production performance, adaptability, survivability and hatchability under heat stress (HS) (Fathi et al., 2022).

Drinker system management of the heat-stressed flock 

The performance of poultry during heat stress is influenced by water temperature, the height of drinkers and their shape (Orakpoghenor et al., 2020). Water consumption is higher in nipple drinkers positioned slightly above the chick’s eye level compared to those set lower. Chickens find it difficult to bend down and drink from lower nipple drinkers (Ranjan et al., 2019). During heat stress, using wider and deeper drinkers is beneficial as they allow birds to immerse not only their beaks but also their entire faces, helping to dissipate more heat. Providing cool water at 10-12°C is advantageous for poultry; therefore, water tanks and pipes should be protected from direct sunlight to prevent the water from warming up. Poultry should always have access to cool, clean water below 25°C, ideally with ice, to help maintain their body temperatures during periods of heat stress (Park et al., 2015).

To support the birds during heat stress, ensure they have ad libitum access to clean, cool water, and consider adding ice to the water. It is important to increase both the space and number of drinkers to guarantee a sufficient supply. During the summer, opt for water troughs with a high flow rate instead of nipple or bell-type drinkers, and position water tanks in shaded areas. This will enhance water intake and help the birds stay cool (Abbas et al., 2017).

Diet formulation of heat stressed flock

During heat stress, poultry typically experience reduced feed consumption and nutrient intake, which negatively affects their performance and productivity. Therefore, adjusting nutrient composition to encourage feed intake is crucial. Implementing feeding strategies that maximize intake, minimize heat load, and mitigate the adverse effects of heat stress is essential for effective nutritional management in high-temperature conditions (Oke et al., 2021). Syafwan et al. (2011) highlighted several feeding strategies to reduce heat load in poultry, including restricting feeding during hot periods, offering choice feeding of low protein or energy-rich ingredients, supplements, providing feeds with different particle sizes or structures to slow digestion, and feeding wet diets to simultaneously promote water intake.

Higher energy rations

Supplementing feeds with fats and oils is an effective strategy for managing heat stress in poultry. These ingredients provide high energy with a lower heat increment compared to proteins and carbohydrates, making them an efficient source of metabolizable energy (Daghir, 2008). Fats and oils are also crucial for the absorption of fat-soluble vitamins and improving nutrient digestibility. In heat-stressed poultry, increasing fat content in the diet promotes feed intake, enhances productivity, reduces heat load, and lowers the specific dynamic effect of rations, aiding in heat stress mitigation (Attia et al., 2021).

Amino acids and protein management in diet

The use of feed-grade amino acids to supplement poultry diets has significantly increased in recent times. Providing amino acids to meet the nutritional needs of poultry supports productivity, intestinal health, immune response, behaviour, and overall welfare (Lee et al., 2023). Additionally, maintaining an appropriate amino acid balance and ensuring an adequate supply, especially of limiting amino acids such as arginine and lysine, is highly beneficial in minimizing the effects of heat stress (Saeed et al., 2019). Sulphur-containing amino acids like methionine and cysteine are important in poultry nutrition. Supplementing with methionine has been shown to decrease muscle oxidation and improve tissue antioxidant status in heat-stressed broilers (Zeitz et al., 2020). Glycine, a conditionally indispensable amino acid in poultry, is essential for enhancing production performance and alleviating oxidative stress and intestinal dysfunction in heat-stressed birds (Deng et al., 2022).

A higher protein level in the diet increases heat production in birds, leading to an elevated heat load and disrupting the ionic balance. The use of reduced crude protein diets is an effective nutritional technique for feeding heat-stressed birds. Minimizes the use of high-protein feed ingredients, lowers nitrogen excretion, alters manure composition, reduces gaseous emissions, and ultimately decreases the carbon footprint and environmental impact of feed production (Cappelaere et al., 2021).

Supplementation of vitamins and minerals

Vitamin supplementation is highly beneficial during heat stress in poultry, as most vitamins serve as anti-stressors, antioxidants, immunomodulators, anti-inflammatories, gut protectants and growth promoters. Chickens have limited endogenous synthesis of vitamins, particularly under heat stress, as high ambient temperatures can decrease their biosynthesis, and retention and alter metabolic functions (Khan et al., 2012). Vitamins A, B, D, E, and C are commonly used to enhance immunocompetence and antioxidant responses during heat stress in poultry. For example, Vitamin A supplementation has been shown to increase feed intake, laying rate and egg weight in laying hens, while also boosting the proportion of peripheral T lymphocytes, thereby improving both laying performance and immune function in heat-stressed hens (Lin et al., 2002). Supplementing with Vitamin C at approximately 250 mg/kg feed has been optimized to enhance production performance, nutrient digestibility, immune responses, and antioxidant capacity in heat-stressed poultry (Khan et al., 2012). Vitamin E, a key antioxidant in the body, provides protective effects during heat stress, mitigating negative impacts on growth performance, productivity, nutrient digestibility, immunity, and the antioxidant profile in poultry (Khan et al., 2012; Niu et al., 2009). Combining vitamins is generally more effective than using a single vitamin to alleviate heat stress in poultry. Supplementing with both vitamins C and E is more beneficial than using each individually, due to their synergistic effects and antioxidant properties in combating heat stress (Attia et al., 2017).

Decreased feed intake leads to insufficient mineral fulfilment in heat-stressed birds. Minerals are essential for cellular and biological functions, support growth and productivity, enhance nutrient utilization, boost immunity, and reduce oxidative stress in heat-stressed poultry (Mir et al., 2018). Heat stress causes respiratory alkalosis, leading to a negative mineral balance and increased loss of sodium and potassium ions during excretion in chickens (Ajakaiye et al., 2011). This increased mineral excretion results in acid-base imbalance, which can be mitigated by supplementing appropriate minerals at various production stages. For example, adding potassium chloride to the drinking water of heat-stressed chickens significantly improves body weight gain lowers body temperature and reduces blood pH, thereby enhancing the bird’s physiological adaptation to heat stress (Ahmad et al., 2008). Zinc offers protective effects during heat stress by eliminating reactive oxygen species, enhancing antioxidant ability, and reducing heat shock response. Additionally, zinc supplementation reduced plasma corticosterone levels, a stress biomarker, and boosted egg production and body weight in turkey breeders during summer heat (Bozakova, 2010; Bozakova et al., 2011). Selenium and chromium are both crucial for alleviating heat stress in poultry. Selenium boosts antioxidant defences and immune function, enhancing production and egg quality (Habibian et al., 2015). Chromium, which is increased in excretion during heat stress, improves production performance, nutrient digestibility, immune response, and oxidative stability (Khan et al., 2014). Thus, in addition to the mentioned minerals, several trace elements such as calcium, phosphorus, copper, iron, sodium, potassium, magnesium, and iodine have been studied and found beneficial for mitigating heat stress in poultry (Mir et al., 2018).

Use of phytochemicals/herbal compounds

Recently, various plant-based and alternative substances with bioactive properties have been used as feed additives to mitigate heat stress in poultry. A bibliometric study highlighted that substances such as flavonoids, probiotic mixes, curcumin, resveratrol, essential oils and plant extracts are beneficial dietary supplements for alleviating heat stress (Uyanga et al., 2023). Bioactive agents like resveratrol, curcumin, and quercetin activate vitagenes and regulate the antioxidant defence system, particularly the Nrf2 signalling pathway, to reduce heat stress-induced oxidative stress in poultry (Madkour et al., 2022).

Supplementation of electrolytes

Electrolyte supplementation has proven effective in maintaining acid-base balance in birds reared during hot summer conditions (Abbas et al., 2021). Electrolytes are crucial for maintaining ionic and water balance in living systems, and their requirements must be considered collectively to achieve homeostasis. Maintaining acid-base balance is essential to prevent the harmful effects of heat stress, as it is influenced by both environmental and nutritional factors. High anion levels (e.g., Cl^–) can lead to acidemia, while high cation levels (e.g., Na⁺, K⁺) can cause alkalemia, both of which can negatively affect poultry performance. Dietary electrolyte balance (DEB) can be calculated using established equations, ensuring that sodium, potassium, and chloride concentrations remain within appropriate ranges. However, physiological stress, such as heat stress, can disrupt this balance in poultry (Abbas et al., 2017).

Supplementing the diet or water with salts like NaHCO₃, NaCl, potassium bicarbonate, KCl, and ammonium chloride can increase water intake in heat-stressed birds, helping to maintain electrolyte balance (Abbas et al., 2017 and Abbas et al., 2021).

Feeding management

Fasting during hot hours reduces metabolic heat output from nutrient digestion, absorption and metabolism and it helps keep birds calm (Saeed et al., 2019). It’s unclear if switching to a coarsely ground diet helps broilers cope with heat stress by improving digestion and reducing heat. Coarse particles increase water retention in the gut, which can reduce the amount of water in droppings. This may help with heat loss through panting. However, it also means that providing extra water is important for heat-stressed broilers. Few studies describe the impact of wet feeding on digestive efficiency and performance in poultry, highlighting how increased moisture can reduce digesta viscosity and improve nutrient absorption, which is beneficial for managing heat stress.

In ovo feeding

However, there are limited studies on in ovo feeding for evaluating thermotolerance, and further research is needed. Recent studies have explored in ovo feeding of amino acids to assess the effects of heat stress in chickens. Supplementation with in ovo L-leucine or methionine has been shown to enhance thermotolerance by increasing feed intake, improving body temperature regulation, boosting immunity-related genes, and modifying antioxidant indices in chickens (Elnesr et al., 2019).

Management of housing and environment 

The environment and the design of the poultry house are crucial for reducing heat stress during heat waves. To minimize the negative effects of heat stress, it is essential to ensure an easy flow of air into and out of the poultry house. By facilitating proper air circulation, the impact of heat stress can be significantly reduced (Nawab et al., 2018). In hot and humid environments, it is crucial to have open-style houses with proper shading, adequate air circulation, and sufficient water intake. The house should also be oriented in the east-west direction to optimize airflow and reduce heat stress (Oloyo and Ojerinde, 2020). Adequate ventilation is essential, as air movement helps remove the build-up of ammonia, carbon dioxide and moisture from the poultry sheds (Nawab et al., 2018). Ventilation equipment should be installed and maintained correctly. It is also important to have standby generators and additional ventilation fans to address emergency situations, such as power outages (Kapetanov et al., 2016). Another important element in preventing heat build-up is the condition of the roofing. The roofs of poultry houses should be kept clean and dust-free. A shiny roof surface is more effective at reflecting solar radiation than a dark or rusty roof. To enhance reflection, metallic zinc paint or aluminium roofing can be applied. Additionally, evaporative panels are used in broiler houses to help alleviate the negative effects of heat stress (Cayli et al., 2021).

Grass cover on the grounds surrounding the poultry house can help reduce the reflection of sunlight into the house. Additionally, continuous trimming of vegetation is necessary to ensure proper air movement and shade trees should be strategically placed so they do not obstruct air circulation (Nawab et al., 2018). Stocking density should be reduced during hot weather to prevent improper ventilation, which can occur with high stocking rates. During heat stress, metabolic heat produced by the birds combined with decreased heat loss due to poor ventilation can raise the temperature in the poultry house. Therefore, floor space should be adjusted based on the intensity of heat stress conditions (Donald and William, 2002).

Conclusion

It is concluded in this review that heat stress adversely affects the health and performance of birds and these adverse effects can be ameliorated by utilisation of naked neck and frizzle genes in high ambient temperatures plays an important role in maintaining production from layer lines. Designing poultry houses, including ventilation, sprinkling, and shading is important in reducing the effects of heat stress. Nutritional manipulation i.e. formulation according to the metabolic condition of the birds as well as inclusion of feed additives, like antioxidants, vitamins, minerals, probiotics, prebiotics, essential oils, organic acids and water supplementation with electrolytes is essential for health and performance.

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