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.
A high respiratory frequency is often a good sign the birds is trying to loose heat. Photo: Marcel Berendsen
7 actions to combat heat stress
- Air circulation around the birds for more oxygen and cooling; at least 4m3 per kg live weight and at least 1 m/s airspeed
- Easily accessible drinking water to compensate for loss of moisture; continuous fresh and cold water
- Cooling to reduce temperature; temperature + RH = 90 +age in weeks
- Adjust feed schedule or composition; less metabolic heat production by replacing some carbs with fat and crude protein by easily digestible protein
- Extra vitamin C to encourage reduction of stress hormones; 300 grams/1000 liter water
- Extra electrolytes to counteract body acidification and supplement electrolytes; add up to 0.3 percent KCI to drinking water
- Lower stocking density for less overall heat production inside the house; max 36 kg live weight per m2
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