With a core temperature of 41°C, one would think that broilers can withstand heat pretty well. Unfortunately heat stress is a serious problem as the birds cannot sweat and can only get rid of excess heat by evaporating moisture during respiration. In other words, they have a very limited cooling system.
Losing heat will become even more problematic with the combination of high temperature (+30°C) and high relative humidity. It’s a deadly combination. Acute heat stress, during heat spells in moderate climates, easily leads to death caused by lack of oxygen and heart failure. In slightly lower temperatures and humidity, the birds will be constantly strained to get their temperature down. However, this strain by extra respiratory frequency, will in turn lead to more heat production. Heat stress will impact performance and lead to a higher overall mortality.