- ✓Recognise a bird suffering from heat and understand the role of humidity
- ✓Use air speed to lower the felt temperature
- ✓Apply the hot-weather action plan: curtains, circulation fans, misting, feed, density
Recognising heat stress
In strong heat, the broiler pants (beak open), spreads its wings, eats less and can die of heat stroke, especially the heaviest birds at the end of the flock. A bird that eats less grows less: heat costs weight long before it costs deaths.
The recommended temperatures after 21 days (24 to 26 °C, then 21 to 23 °C at 28 days, then 19 to 21 °C or as cool as possible) are often exceeded in an Ivorian open-sided house. You cannot cool the air as in a closed house: you act on moving air, shade, water and meal times.
Moving air cools
The table shows the temperature felt by a bird over 28 days old according to the speed of the air over it. Two lessons: air speed gains you many degrees, and humidity makes the heat worse.
| Temperature and humidity | Still air | Air at 1.1 m/s | Air at 2.5 m/s |
|---|---|---|---|
| 35 °C, 50% humidity | 35 °C | 26.6 °C | 22.2 °C |
| 35 °C, 70% humidity | 38.3 °C | 30.5 °C | 25 °C |
| 32 °C, 70% humidity | 35 °C | 28.8 °C | 23.3 °C |
| 29 °C, 80% humidity | 33.3 °C | 28.8 °C | 23.8 °C |
Source: Cobb.
Example: at 35 °C with 70% humidity, a bird in still air feels 38.3 °C; with air at 2.5 m/s, it feels only 25 °C. After 28 days, the recommended air speed over the birds is 1.75 to 2.5 m/s. Careful: before 14 days, no draught at all (lesson 3 of this track).
The hot-weather action plan
- Curtains: open them as low as possible and on both sides to get a maximum of air over the birds (after 14 days).
- In the morning, open the downwind side first.
- Circulation fans of at least 90 cm, placed about 1 m above the floor, tilted to push the air in the direction of the wind.
- Misting: start it at around 28 °C, never when the air is already very humid (over 70%).
- Feed: raise the feeders in the hot hours; cool water at all times.
- Get the birds up: walk slowly through the house; they stand up, air circulates and they go to drink.
- Density: reduce the number of birds per m² in the hot season (8 to 10 per m²).
Source: Cobb.
Misting: useful, but not always
Misting cools by evaporating water. It works when the air is dry; when the air is already very humid (over 70%), the water no longer evaporates, humidity rises and, as the table shows, the felt heat increases. The litter gets wet too. So check the hygrometer before misting: in the rainy season or early in the morning, the air is often already too humid.
Start misting at around 28 °C. Never mist above 70% humidity.
Eating in the cool hours
Digestion produces heat. In strong heat, raise the feeders about 6 hours before the hottest time of day and let the birds eat in the cool hours: early morning and evening. In an open-sided house, lighting mostly follows daylight; the natural night lets the birds rest in the cool.
Meanwhile, water never stops: shaded tanks, a 48-hour reserve, clean and plentiful drinkers.
For the entrepreneur
- ›Equip the house with circulation fans of at least 90 cm: they are the main weapon against heat in an open-sided house.
- ›In the hot season, reduce density to 8 to 10 birds per m²: fewer birds, but more birds sold.
- ›Install a hygrometer: it tells you when misting helps and when it makes things worse.
For the technician
- ›After 14 days, open the curtains low and on both sides; in the morning, the downwind side first.
- ›Start misting at around 28 °C, never above 70% humidity.
- ›Raise the feeders in the hot hours and walk slowly through the house to get the birds up and drinking.
The 3 questions to ask your technician this week
- What time did you raise the feeders today, and what time did you lower them again?
- What humidity did the hygrometer show when misting started?
- How many birds are panting in the hot hours, and have there been any heat deaths?
Key points
- •Heat stress: panting, spread wings, less feed eaten; the heaviest birds die first.
- •Moving air cools: at 35 °C and 70% humidity, 38.3 °C felt in still air, 25 °C with air at 2.5 m/s.
- •Humidity makes the felt heat worse.
- •After 28 days: 1.75 to 2.5 m/s over the birds; before 14 days: no draught at all.
- •Fans of at least 90 cm about 1 m above the floor, in the direction of the wind; misting from 28 °C, never above 70% humidity.
- •Feeders raised in the hot hours, cool water at all times, density reduced in the hot season.