Keeping birds comfortable throughout their lives is a key way to ensure productive performance, and hot weather can lead to higher mortality related to heat stress.
Birds that are too hot will soon begin to lose daily weight gains and record poorer feed conversion ratios.
Stress levels will also spike, which can lead to secondary issues like a lower immune response to disease challenges.
A trend in recent years of warmer, wetter winters and hotter summers can mean some broiler units struggle to ventilate just when they need to be at maximum capacity.
“There’s an optimum level where birds are taking in a good amount of energy and using very little for maintenance,” explains Brendan Graaf, a broiler specialist with Cobb Europe.
“This is where we want to keep them, so they have lots of surplus energy for growth and performance.”
We asked Mr Graaf for his top tips for managing birds when temperatures rise.
1. Measure ambient air temperature
Broilers need to consume about 260kcal/kg every day to maintain target growth levels, compared with 55kcal/kg in humans.
Roughly 25% of that consumption is used for the bird’s essential functions, including growth, and 75% is given off as metabolic heat.
They release this into the air around them, which is why ambient air temperature is important, and through the evaporation of moisture from the respiratory tract – known as latent heat loss.
Latent heat loss is influenced by relative humidity in the shed environment.
Birds rely more on latent heat loss to control their body temperature – about a 60:40 split.
2. Look for signs that birds are too hot
One of the first indicators that birds are too warm is the spreading of both wings and legs.
Panting is another obvious sign. Even if only a few in a shed are doing so, it is likely most birds are in the upper limits of their thermal comfort zone, and production is hampered.
If a bird’s body temperature rises more than four degrees above its normal level, it will succumb to heat stress.
- Monitor regularly Temperatures might vary between the sensor, typically at least a metre above bird level, and the actual heat on the level where the broilers are, particularly when stocking densities are higher. That’s why observing birds is so important.
- Spread out the flock If warm weather is forecast, consider lowering your stocking densities by placing fewer birds to help alleviate pressure on ventilation.
- Think about lighting Hot temperatures make birds eat less, so it’s vital to adjust lighting regimes to give birds a chance to catch up on feeding when the weather is cooler. Lights should be switched off as late as possible, and timing should be set at the beginning of the cycle so that birds are used to it.
- Get timing right On very hot days, start ventilating earlier in the morning and keep ventilation on later into the evening to give birds the best chance of cooling down.
A good place to start is with temperature set points – most systems work off this measure, though some work off relative humidity.
Cobb has comprehensive guidelines in its broiler handbooks, and over the past 10 years or so, those maximum recommended temperatures have been brought down.
They are based on age until 14 days, and from then on, stocking density becomes the main factor in determining temperatures.
3. Monitor shed temperatures
High temperatures are largely controlled in UK sheds by transitional ventilation, where cooler, fresh air is drawn into units through side inlets.
In Europe, sheds with tunnel ventilation are more common.
Whatever type of shed, the key is to get good wind speed across birds.
Farmers should not worry that birds go “flat” and become less active; at least 25% will continue to move and take feed and water.
“They will be cool, and you can give them time later in the evening to be able to catch up or compensate on feed intake they didn’t get during the day when it was hot,” says Mr Graaf.
What to be aware of in tunnel-ventilated sheds
European poultry sheds tend to be very wide with relatively tall roofing.
Using tunnel ventilation in hot conditions can lead to a cooler climate at the front of a shed and a warmer one at the back.
Birds will naturally migrate towards the cooler part of sheds, increasing stocking densities and potentially crowding feeders and drinkers.
Migration fences installed in summer can help prevent this, and thereby improve bird uniformity.
What to be aware of in sheds that use side inlets
Side inlets can be trained downwards on to birds to help keep them cool.
Air will be a lot cooler close to the inlet, which can present a similar problem to uneven heating as tunnel ventilation.
“You might get problems with birds migrating closer to the cool air, increasing stocking densities – the result is that birds might actually be warmer in those areas,” says Mr Graaf.
Air movement can be lower close to the side-wall, as well, so it’s essential to monitor bird activity and make management decisions accordingly.
4. Keep an eye on stocking densities
The pressure that hot temperatures present is naturally highest when stocking densities approach their maximum, usually in the days leading up to thinning and before final depopulation.
It is at this time that managers must be most aware of shed environments.
How fogging systems can help
Fogging systems can present an effective way to bring high temperatures under control, but require a good, clean water supply and careful management.
They work by firing a fine mist over birds and the shed’s heat causes the water to evaporate, giving up to a 7C heat reduction.
But for every degree that the temperature drops, relative humidity will increase by 4.5%.
For example, in a shed where the relative humidity is at 50%, cooling the shed by 7C would result in relative humidity rising to 85%.
Above 85% humidity, the birds’ respiratory cooling becomes ineffective, so fogging systems should only be used while fans are in full transitional mode.