Dr. Sathya Sooryan
MVSc (Animal Nutrition), PGDOH, Senior Product Manager, email@example.com
Dr. SanjayMVSc (Animal Nutrition), Technical Executive, Vetogen Animal Health, firstname.lastname@example.org
As the sun rises high and the days stretch long, the cornerstone of modern agriculture, the poultry industry face a season of despair. Summer, with its sweltering heat and endless sunshine, presents a myriad of challenges to the commercial poultryfarms,which provides a significant source of protein to populations around the globe. As temperatures rise, the heat has a serious impact on thehealth and productivity of the bird leading to profoundimpact on profitability of commercial poultry farms. To address these challenges, farmers must be diligent in their understanding of the three consequences of heat stress which impacts the health and productivity of birds. They also should be aware of management practices and steps to mitigate the impact of heat stress on their flocks. This article focuses on 3 core areas and addresses varieties of challengesfaced by commercial poultry due to heat stress.
When is your bird Heat Stressed?
If birds have difficulty in achieving a balance between body heat production and body heat loss they enter into heat stress, undergo physiological changes and exhibit behavioural response (Image No. 1). This can occur at all ages and in all types of poultry.
Image No. 1:
How birds respond to different ambient temperature
The temperature ranges within which poultry birds maintain their body temperature is understood as Thermo neutral zone. This range lies between 21 to 26.7 °C. When upper critical temperature i.e., 26.7 °C is exceeded, birds must lose heat actively by panting. Beyond 29.4 °C, birds reduce their feed consumption and as temperature cross 32.2 °C, the egg size and production decreases in layers.Beyond 35 °C, hens start losing weight. If heat production still increases beyond maximum heat losses by the bird’s body, either in intensity (acute heat stress) or over long periods (chronic heat stress) birds will die. At 32 °C and Relative humidity 50% are the benchmarks for beginning of Heat stress (Image No. 2).
Image No. 2: How birds respond to different ambient temperature
Heat Stress = Panting, No! its loss of electrolytes
Panting in heat-stressed bird is a common visible symptom which allows bird to dissipate body heat, but along with heat, water and crucial electrolytes are lost in the process which alters the acid-base balance in blood plasma and ultimately leads to respiratory alkalosis. During respiratory alkalosis, birds excrete a higher amount of bicarbonate ions from the kidney to restore normal blood pH. These bicarbonate ions are further coupled with Na+ and K+ ions before being excreted through the kidney. Ultimately, the loss of ions results in an acid-base imbalanceTong et al. (2020).
A change in acid-base balance in the blood plasma of birds can have a significant impact on poultry health and production. If the pH level of the blood becomes too acidic or too alkaline, itcauses metabolic disorders and reduce the birds’ ability to absorb nutrients from their feed. This can lead to decreased growth rates, reduced egg production, and increased susceptibility to diseases. Furthermore, changes in acid-base balance can affect the activity of enzymes and metabolic pathways in the birds, leading to further health complications.To maintain optimal poultry health and production, it is important to monitor and regulate the acid-base balance in the birds’ blood plasma through proper nutrition and management practices.
This acid-base imbalance can be recovered by supplementation of electrolytes such as NH4Cl, NaHCO3, and KCl. Sodium and potassium supplementation is preferred in heat-stressed birds to increase the blood pH and blood HCO3−, while chloride is supplemented to reduce these parameters. A higher range of dietary electrolyte balance (DEB), i.e., 200–300 mEq/kg, has been suggested to be effective in ameliorating the detrimental effects of heat stress in poultryYahav, S. (2018).
Heat doesn’t kill the bird it just suppresses immunity
Increasing temperature creates many changes in bird’s body which leads to suppressed immunity which increase the chances of disease and mortality in flock. High Temperaturecause oxidative stress in birds, leading to the production of reactive oxygen species (ROS) and oxidative damage to cells. This compromises the birds’ immune system by decreasing the production and function of immune cells, including T cells, B cells, and macrophages. Additionally, heat stress affects the production of antibodies, cytokines, and other immune molecules, further suppressing the birds’ immune responseYahav, S. (2018).
Another way in which heat stress affects immunity in poultry birds is by increasing their susceptibility to bacterial and viral infections. For example, heat-stressed birds are more likely to contract infectious bronchitis virus (IBV), a highly contagious disease that affects the respiratory system. In addition, high temperatures can increase the replication rate of some bacteria, such as Escherichia coli and Salmonella, leading to more severe infections in the birdsSharma, N. K., & Singh, N. K. (2016).
To mitigate the negative effects of heat stress on the immune system of commercial poultry birds, it is important to provide appropriate management strategies. One such strategy is to provide adequate ventilation and cooling in poultry houses. This can be achieved through the use of fans, misters, and evaporative cooling systems. Additionally, it is important to provide clean and cool drinking water, as water intake is essential for maintaining the birds’ immune system.Furthermore, providing proper nutrition to birds during heat stress is essential. For example, supplementation of antioxidants such as vitamins E, C and Selenium can help reduce the production of ROS and minimize oxidative damage to cells. Moreover, feeding birds with probiotics, prebiotics, and immune-enhancing compounds such as proven herbs can help improve their immune function during heat stressAlabi O. J.(2018); Kargaret al., (2021).
Heat doesn’t reduce productivity it just suppresses gut health and alter gut morphology.
Heat stress affects the gut health of poultry birds in several ways, including the disruption of gut microbiota, intestinal morphology, nutrient absorption, and gut immune function. One of the major ways in which heat stress affects gut health in poultry birds is by altering the gut microbiota composition. The high temperatures create a favourable environment for the growth of harmful bacteria, leading to an increase in the pathogenic load of the gut. This can result in a disruption of the balance between beneficial and harmful bacteria, leading to dysbiosis.Wang, Y., et al. (2020)Heat stress decreased populations of beneficial bacteria (Lactobacillus and Bifidobacterium) in the intestine which was replaced by harmful bacteria like Coliforms and ClostridiumLiu, H., Iqbal, Z., & Xiao, S. (2021).
Additionally, heat stress can lead to changes in the intestinal morphology, including decreased tight junction protein expression (leaky gut) (Image No. 3), decrease in immunoglobulin A-secreting cells, villus height and an increase in crypt depth, which can further exacerbate dysbiosis and entry of bacteria to system.These changes lead to a decrease in digestibility of the feed and low availability of nutrients for absorption from the intestinal mucosa to the blood. Physiological changes resulting from heat stress allow the pathogenic bacteria to enter the bloodstream by crossing the intestinal lumen to cause septicaemia. In this manner, heat stress leads to lower performance, less egg production, low meat yield, retarded immunity status, and low reproductive performanceHashemi, S. R. (2019).
The feed intake is reduced and water intake is enhanced, which has a negative impact on the absorption of nutrients being produced by the microbiota in the intestinal lumen. Additionally, the secretion and motility of the intestine increases and nutrient absorption decreases. Production of digestive enzymes in the intestinal lumen is decreased by the heat stress, which adversely affects the intestinal mucosa leading to oxidative stress and inflammation. Heat stress also affects the nutrient absorption capacity of the gut, leading to reduced feed efficiency and growth performance. High temperatures can reduce the expression of nutrient transporters in the gut, leading to a decreased uptake of nutrients such as amino acids, glucose, and electrolytes. This can lead to a decrease in feed efficiency and growth performance, which can result in significant economic losses for farmersR. I. N. Gresseet al (2017); R. J. Collieret al (2017).
To mitigate the negative effects of heat stress on gut health in commercial poultry birds, appropriate management strategies must be implemented as described above. Additionally, farmers should provide clean, cool drinking water and high-quality feed that contains probiotics, prebiotics, and immune-enhancing compounds such as herbs and essential oils to support gut health. The use of feed additives such as organic acids, enzymes, and phytogenic compounds can also help improve nutrient absorption and gut health in heat-stressed birdsT. J. Applegateet al (2014); N. A. Mayahiet al (2017).
Image No. 3: Effect of heat stress on intestinal health and immune system
Heat stress is a major challenge for the commercial poultry industry, particularly during the hot summer months. The negative impact of heat stress on the health and productivity of birds can be significant, leading to three major changes effecting productivity and profitability of commercial poultry farm that is loss of electrolyte, decreased immunity, suppressed gut health. However, by implementing appropriate mitigation strategies focusing these three core areas, farmers can significantly reduce the impact of heat stress on their flocks. By providing adequate ventilation, ensuring access to clean water, and managing water, feed and nutrition, farmers can maintain the health, performance and profitability of the farm.