Dr.Partha P. Biswas
M.Sc.,Ph.D.,F.Z.S.,F.Z.S.I.
Former Asso. Professor & H.O.D.,
Dept. of Zoology, R.K.Mission V.C.College,
Kolkata ,W.Bengal.
Senior Consultant, Aqua-Vet inputs,
Fin-O-Wing Formulations, Kolkata-700084

The chicken industry is becoming more vulnerable to environmental shifts, particularly high temperatures. Open-sided poultry species are susceptible to heat stress, negatively impacting growth and productivity. Factors determining heat stress include temperature radiation, humidity, metabolic rate, age, and duration. Modern commercial broilers are more sensitive to heat stress, making understanding and controlling environmental conditions crucial for poultry production and health. High temperatures in birds reduce antioxidant capacity, requiring food handling and expensive cooling. Understanding and controlling environmental conditions is crucial for poultry production and health.

Thermoregulatory Device in Chicken
Unlike mammals, birds do not have sweat glands, but they have developed a number of behavioral adaptations to cope with heat, including increased breathing rate, panting and raised wings. Commercial poultry prioritize high production, making broilers more sensitive to environmental stresses, and affecting meat quality and immune problems. Under conditions of heat stress, metabolic heat increases, and the animal succumbs to hyperthermia. In summary, it can be concluded that high ambient temperature outside the thermoneutral region during the production phase has a bad effect on meat production, meat quality and causes serious immune problems in broilers.

Heat Shock Proteins of Poultry Birds During Heat Stress
Heat shock proteins (HSPs) are stress proteins found in all living organisms that are activated by high environmental temperatures to protect cells from stressors such as heat. The 70 kDa heat shock proteins (HSP70) are a family of proteins known for their potential role in thermotolerance and widely regarded as cellular thermometers. Over expression of HSP70 has been observed under oxidative stress, leading to mitochondrial reactive oxygen species scavenging and pulmonary endothelial protection against bacterial toxins. They keep cells in order by synthesizing other proteins, attract immune cells and participate in protein assembly and degradation. Higher HSP expression is associated with better heat tolerance and is produced by all living organisms in high temperature environments.

Effects of Heat Stress in Poultry Birds
Reduced voluntary feed intake which affects the functionality of the entire digestive system High environmental temperatures activate the hypothalamus–pituitary axis, brain-gut axis and elevate plasma corticosterone concentrations, affecting the digestive system’s functionality.

This leads to changes in motility, flux patterns, secretory activity, content viscosity and pH Generation of ROS (reactive oxygen species) and the efficacy of the antioxidant defense system deteriorate. Overproduction of ROS in mitochondria can damage proteins, lipids, and DNA Heat stress can impair the feeding process, nutrient absorption and utilization, although water intake increases rapidly Upregulation of adipokines secretion (leptin and adiponectin) and the expression of their receptors can negatively regulate feed intake and calorie consumption thus resulting in decreased metabolic heat production The decline in trypsin, chymotrypsin and amylase (intestinal secretion) due to reduced feed intake often results in impairment of digestive functionality, nutrient digestibility Hypoperfusion and an increase in blood flow to the skin surface occur as an adaptive response of the circulatory system to stabilize blood pressure and promote heat loss It is known that heat challenge has an immune-suppressive effect.

Use of Dietary Phytochemicals to Reduce Heat Stress
Experimental studies on poultry birds suggest phytochemical ingestion may reduce heat stress effects. These phytochemicals can directly or indirectly influence genes and metabolic pathways, with stress reduction linked to antioxidant qualities.

Fig.3: The chicken’s response to being overheated. Chickens raised in high temperatures produce more reactive oxygen species and show signs of immunological inflammation in addition to consuming less food.

Mitigating Heat Stress Using Epigallocatechin-3-Gallate (EGCG), A Secondary Metabolite in Green Tea

Green tea’s most prevalent catechin, EGCG, is thought to be its most bioactive ingredient and possesses potent antioxidant properties. The primary cause of heat stress-induced oxidative stress in poultry is damage to tissues and cells, which is mostly manifested in an increase in MDA (malondialdehyde) concentration in such tissues and cells. It has been demonstrated that adding the polyphenol EGCG to broilers housed in thermoneutral environments may increase their antioxidant capacity. Acutely heat-stressed broilers may have greater antioxidant capacity and less oxidative damage in their muscles because EGCG may activate the Nrf2 signaling pathway.

Reducing Heat Stress in Broiler Chickens With Additional Ginger (Zingiber Officinale) and Onion (Allium Cepa)

Onion and its derivatives including saponins, aglycones, quercetin, cepaenes, flavonoids, organosulfurs, and phenolic compounds showed various pharmacological properties and therapeutic effects.When broilers are heat stressed, the combination of onion and ginger supplements increases the nutrition of the groups more than no supplementation.

According to research results, growth performance, carcass quality, antioxidant levels and immune system response of broilers are improved when fed 10 g of ginger and and 2.5 g of onion during heat stress. Ginger contains substances with powerful antibacterial and antioxidant properties, including chagaol, ginger diol and ginger diol. Ginger (2%) added to broilers suffering from heat stress significantly improved blood biochemical parameters and growth indicators compared to the control group.

Seeds of Black Cumin (Nigella Sativa) improve Bird’s Ability to Live in Heat-stressed Conditions

Black cumin seeds have been shown to have pharmacological and antibacterial properties and also contain drug-like compounds. The volatile oil (0.4-0.45%) contains saturated fatty acids, which include: nigellone, which is the only component of the carbonyl fraction. oil, thymoquinone (TQ), thymohydroquinone (THQ), dithymoquinone, thymol, carvacrol, α and β-pinene, d-limonene, d-citronellol, carvacrol, t-anethole, 4-terpineol and longifolin etc. Thymoquinone improves hatchability, pos-thatching performance and antioxidant activity of thermally stressed broiler embryos. Black cumin extract has been shown in trials to reduce serum MDA levels and protect against oxidative stress.

Hot Red Pepper (HRP) Reduces Heat Exhaustion in Birds

Ascorbic acid, or vitamin C, is abundant in capsaicin, a terpenoid found in HRP that helps prevent heat exhaustion in birds. Carotenoids, which are rich in vitamins E, C, and provitamin A (beta carotene), are known to have powerful antioxidant qualities that help prevent the damaging effects of free radicals and, in certain situations, oxidative stress, which can lead to cell death in broilers. Furthermore, it has been found that adding capsaicin, an active ingredient in red pepper that is present in grill feed at a dose of 50 mg/kg, can lessen the harmful effects of heat stress.

Moringa (Moringa Oleifera)helps to Survive Birds Under Heat Stress

Moringa leaves contain high levels of total polyphenols (260mg/100g), b-carotene (34mg/100g), kaempferol (34mg/100g), quercetin (100mg/100g), as well as a total antioxidant capacity of 260mg/100g. Kaempferol and quercetin are the flavonoids present in moringa leaves and possess strong antioxidants. It has been found that 0.3% incorporation of M. oleifera leaf meal improves the performance and physiological parameters of broilers and also helped the birds survive under heat stress.

THYME (THYMUS VULGAIS) Protects Chicks Against Heat Stress

The two most important bioactive compounds in this plant are carvacrol and thymol, which may be the primary source of thyme’s pharmacological actions. Thus research has identified linalool, thymol, carvacrol, gamma-terpineol, and geraniol as the primary components of thyme. Dietary thyme essential oil (150–200 mg/kg) is more effective at shielding chicks from the harmful effects of heat stress while also enhancing immunological function and development performance. One material that may be able to improve growth in broilers located in hot climates is thyme oil.

Coriander (Coriandrum Sativum) Seed in Ameliorating the Impact of Thermal Challenges

According to research, broilers under heat stress that are fed 2% coriander seed have higher feed intake, weight gain, reduced panting, and higher levels of corticosterone. The broilers’ poor intestinal absorptive capacity and shape may be connected to the rise in corticosterone levels during stress. Furthermore, according to a different study, adding 2% coriander to the diet helps broiler birds by lessening the effects of heat shock. The supplement, according to the author, benefitted broilers that were experiencing heat stress and enhanced their blood parameters, immunity, and overall performance.

Cinnamon (Cinnamomum Zeylanicum) Powder as Antioxidant in Thermally Challenged Birds

The common herbal plant, cinnamon contains different active phenolic compounds, which include flavones, catechin, isoflavones, flavonoids and other phenolics. The main bioactive constituent of cinnamon is cinnamaldehyde. The phenolic components function as antioxidants and can effectively scavenge ROS. Cinnamon supplements help in homeostasis due to the reduced pH caused by heat stress. It has also been reported that an increase in the activity of CAT, total antioxidant capacity and SOD and a decrease in the MDA when birds were placed in a thermally challenged environment during their finishing phase.

Turmeric (Curcuma Longa) for Heat-stressed Broilers

The yellowish pigments of turmeric, namely demethoxycurcumin, curcumin, and bisdemethoxycurcumin, are commonly referred to as curcumoids. Curcuminoids are an antioxidative compound found in turmeric. Researchers have shown the effects of turmeric powder supplement at 0.3 and 0.6 g/kg when administered to birds under heat stress. The superoxide radicals are neutralized, and there is an increase in the activity of SOD and CAT (ROS-removing enzymes or antioxidant enzymes ) and a decrease in MDA in broilers. The increased level in MDA indicates oxidative damage in liver of heat stressed broilers.

Conclusion
Heat stress can hurt poultry birds by making them grow slower, weakening their immune system, causing intestinal inflammation, and causing other health problems. It can also trigger oxidative process. But using natural substances called phytogenic compounds can help chickens who are raised in hot conditions.But more research is needed to understand the molecular changes made by medicinal herbs and the interactions between their active components, gut microbiota, and gut barriers. By using these approaches, we can improve chicken welfare and make poultry production more sustainable and efficient.

Mr. Naresh Ravi, Project & Development Manager, 

KP Asli Sdn. Bhd, Malaysia I Poultry Enthusiast I WPSA Member

Figure 1.0- (left) Imagined paths of how much carbon we might release this century based on different choices about energy and how economies grow. (right) Predicted rises in temperature compared to the average from 1901-1960, based on which carbon release path we end up on. Image by Katharine Hayhoe, from the 2017 Climate Science Special Report by the U.S. Global Change Research Program.

The increasing menace of climate change profoundly challenges the resilience of environmentally controlled (EC) broiler houses—infrastructures that are precisely built to create an ideal environment for poultry growth. As we gaze into what lies ahead, apprehensions intensify regarding the ability of this EC broiler houses’ to weather the looming climatic challenges catalysed by escalating global temperatures. This year’s record-breaking average global temperatures, such as the unprecedented 17.01°C experienced on July 3, illuminate the reality of this threat —’ . Further, predictive climate models offer robust projections, foretelling a future dominated by more frequent and intense heatwaves if annual carbon emission keeps on increasing as shown in figure 1.0.

In this article, delve into practical strategies to minimize external heat entry, from roofing choices to sidewall materials, ensuring optimal poultry health even in adverse conditions. Additionally, we explore the techniques to efficiently remove internal heat and cool incoming air, a critical aspect as broiler size increases in regions like China and India. By journey’s end, you’ll be equipped with a robust understanding of the pressing need for climate-resilient broiler houses and the solutions available to usher in a new era of poultry farming.

1. Strategies to Reduce Heat Penetration in EC Broiler Houses

Heat mainly enters chicken houses in two ways: through radiation and conduction. Radiative heat involves the absorption of electromagnetic waves. A broiler house with a dark roof or sidewalls absorbs more radiant energy than one with lighter shades. Over time, this can increase internal temperatures, stressing birds and affecting growth rates.
Conduction happens when heat moves through a material due to temperature differences. For example, on hot days, a metal-roofed broiler house can get hot externally, transferring this heat inside and jeopardizing bird comfort and health.

Figure 1.1- Majority of the heat entering the house via radiation. Image by https://ssl.acesag.auburn.edu/poultryventilation/documents/InsulationPVP.pdf

– Roofing: The roof accounts for approximately 70% of the heat entering a broiler house. Choosing the right roofing material is vital. Insulated roofing can minimize solar heat on warm days, benefiting the birds. The efficiency of insulation is rated by its R-value, with higher values indicating better insulation. A commonly used option is 25mm of PU (polyurethane) roofing with an R-value of 6. If you opt for a non-insulated roof, adding an insulating layer in the ceilings can help. However, EC broiler house without any roof insulation or ceiling insulation puts tremendous pressure to the ventilation system as more heat enters the house. For example, a PU roof can maintain internal temperatures around 33.3°C, a notable improvement of 10% from 37.2°C with a non-insulated roof.

Figure 1.2- Example of PU roofing used in poultry farm.
Image by https://agro-house.astino.com.my/astino-swine-structure/

– Sidewalls: Account for the remaining 30% of heat entering the house.

Curtain: While curtain sidewalls are popular due to their cost-effectiveness and flexibility during emergencies, their insulation properties are limited (R-value= 1.5). For instance, during hot summer days, side curtains can let in a lot of heat, which may require additional ventilations to maintain the right temperature for the birds.

Figure 1.3- Example of curtain sided EC broiler house.

Image credit: https://www.taimeichina.com/pid18255954/Poultry-House-Curtain-Poultry-Side-Curtain.htm

Insulated side wall: Besides that, traditional fiberglass batt (R -Value 3.2) side wall insulation offers cost-effectiveness and fire resistance but may settle over time and is susceptible to moisture damage. Modern Spray Foam (R -Value 7.0) insulation ensures comprehensive coverage and acts as a moisture barrier, especially in its closed-cell variant. However, it can be more expensive and might emit VOCs. Structural Insulated Panels (R -Value 4.0) are pre-fabricated units that speed up construction and reduce thermal bridging, though they can be pricier and challenging to modify post-installation.

Figure 1.4 Fiber glass batt insulation.

Image credit: https://www.silvercote.com/products-and-systems/ag-by-silvercote/ag-for-chickens/

Figure 1.5 Spray foam insulation.

Image credit: https://www.agseal.com/commercial-spray-foam-insulation-products/

Figure 1.6 Structural Insulated Panels (SIPs).
Image credit: https://raycore.com/sips-structural-insulated-panels/

Brick wall : Bricks, including hollow bricks (R-Value 1.1), are a traditional and durable option for side walls. Hollow bricks have empty spaces within them, providing some insulation. While they are not as efficient as modern insulation materials, they offer long-lasting structural integrity. For instance, in areas prone to extreme weather conditions, hollow bricks can withstand the elements and contribute to temperature regulation inside the broiler house.

Figure 1.7 Brick wall EC Broiler House
Image credit: Syarikat Sin Long Heng Breeding farm Sdn.Bhd

2. Optimizing Internal Heat Removal
The EC Broiler house gets heat mainly from two aspects: the heat from outside environment which is about 10% and the chickens themselves produce 90% of the heat inside the house. After stopping as much outside heat as possible, we need to get rid of the heat inside. We can do this with good ventilation, like having enough fans capacity. If we don’t have enough fans, it can get too hot inside, even hotter than outside! This can make the chickens very uncomfortable. Ideally, the back of the house shouldn’t be more than 3°C hotter than the front. If it is, then the fans capacity or number of fans are not enough. Currently, our goal is to achieve a wind speed of 3 m/s inside the chicken house, as this will expedite heat removal and provide a wind chill effect for the chickens. However, will 3 m/s be sufficient in the foreseeable future?

In the Asia-Pacific region, there used to be a preference for smaller chickens, with many weighing under two kilograms. However, there’s a trend towards larger birds, especially in China and India. As countries improve disease control and purchasing power, they’re choosing to raise bigger chickens because it’s more efficient. But with bigger chickens and hotter weather, we might need even higher wind speed in the future .

3. Efficient Cooling of the Inflowing Air
Once the challenges of heat entering the chicken house and the removal of internal heat are tackled, it’s crucial to focus on cooling the incoming air. This task is carried out with the help of cooling pads. The farmer should select a cooling pad size that matches the house’s needs, it ensures a wind speed of the cooling pad is around 1.5 to 1.7 m/s to ensure optimum cooling efficiency which is about 75% to 80%.

For optimal pad cooling, it’s crucial to align the total pad area with the fan capacity. This ensures desired cooling efficiency and prevents exceeding a static pressure of 0.10 inches. A frequent error in cooling pad installations is insufficient pad area, leading to high static pressure and inadequate fan performance and cooling.

The true power of the cooling pad lies in its combined effect with tunnel ventilation. The goal is to reduce the incoming hot air to a point where, combined with the wind-chill from tunnel ventilation, the chicken feels as though they’re experiencing temperatures close to 21°C. For instance, if outside air is 35°C and the cooling pad reduces it by about 6.5°C, and tunnel ventilation provides an “effective temperature” drop of another 5.5°C, the chicken would perceive the temperature to be around 23°C  .

Diving deeper, let’s not forget that all cooling pads aren’t made equal. A cooling pad made of paper might absorb and release moisture differently than one made of plastic. It’s like having two different brands of air conditioners; each might need its own settings to work best. So, for a farmer, understanding the type of cooling pad in use is essential to get the best cooling results and keep the birds comfortable.

Figure 1.8- The mechanism of reducing the air that entering the EC chicken house with evaporative cooling pad

Conclusion
The events of 2023 emphasize the need for advanced designs to face rising global temperatures. By grasping heat dynamics and selecting the right materials, we can ensure the health of larger Broiler populations, especially in fast-changing regions like China and India. Adapting to climate change is crucial for the poultry industry’s sustainability.

References are available on request.