Heat Stress and Ventilation

As the summer months approach, so does the blistering temperatures and humidity.  As poultry owners, one of the concerns that consume our thoughts during summer is heat stress because of its negative effects on the welfare of meat birds and laying hens.  So, what exactly happens internally to the birds that cause low productivity, reduced growth and low meat and egg quality?

Let’s look!

Because chickens are homeotherms, much like most animals, they can regulate their body temperature; however, chickens need good ventilation in order to be able to optimize their productivity and remove the ammonia that builds form the litter. 

As heat stress progresses, the deep body temperature rises – this is detected in the hypothalamus (the portion of the brain that controls certain metabolic processes and activities of the Automatic Nervous System) which then sets off behavioral and physiological responses… 

Here are a few to consider:

Look out for your chickens panting.  Chickens will begin to pant which cools the body by evaporative cooling or a loss of water.  With this excessive panting, the respiratory rate of the birds’ increases, which leads to respiratory alkalosis.  What is this? This term describes the mechanism of carbon dioxide and bicarbonate being lost. Why are carbon dioxide and bicarbonate important? These chemical compounds make up the buffer system which helps regulate blood pH. When respiratory alkalosis occurs, plasma pH increases (almost up to 8.0) and intracellular pH becomes acidic, resulting in losing potassium (Goo et al. 2019). 

Big words scaring you? Tell me about it!

Another sign to look out for is the chicken spreading its wings.  This sign indicates that the chicken is hot, and the spreading of its wings helps move heat from the body to the ground. 

Because of respiratory alkalosis setting in, the chicken will stop eating and begin drinking nearly twice as much water as it needs – this results in a lower production of metabolic heat which cools the body down via the gut.  With this increase in water intake, the chicken will begin to have a more water-filled poop, which increases the chance of wet litter and bacteria.

As the chicken decreases in productivity and its health declines, cardiac shunt will occur – the pattern of blood flow in the heart will stray from the normal circuit.  Blood will be pushed away from the gut in order to reduce the production of metabolic heat and will be pushed to the comb in order to release more heat.  With an increase in the reduction of heat, urine excretion will increase which will result in sodium and potassium balance being lost which will cause a loss in acid/base balance (the balance between acid and base within the body helps ensure that the body does not lose energy through such things as excessive panting) (Merck Manual, 2019).

Change is a stressor for chickens and when encountered, the neurogenic system is activated.  Make sure that your coop is well ventilated and provide shade for your birds when the scorching heat is upon us – try and normalize the outdoor conditions.  Also, keep in mind that nutritional supplements like Chicken DeLyte are good in times of stress – it’ll keep both owner and chicken happy and content!

Merck Manual Consumer Version. 2019. Overview of Acid-Base Balance. https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance

Goo D, Kim JH, Park GH, Reyes JBD, Kil DY. Effect of Heat Stress and Stocking Density onGrowth Performance, Breast Meat Quality,and Intestinal Barrier Function in Broiler Chickens. Animals. 2019 [accessed 2019 Jun 24];9(3):107. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6466317/. doi:10.3390/ani9030107

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