The latest avian influenza outbreaks have highlighted the need for improved air quality in naturally ventilated free-range poultry sheds, according to industry experts.

The increased amount of time that free-range birds have had to remain indoors due to avian influenza restrictions has led to reports of negative impacts on flocks. These are often associated with poor air circulation.

Stringent requirements placed on environmentally controlled farm buildings may have seen poultry owners adopt modern ventilation techniques such as humidity sensors and high velocity jet extraction fans but a quarter of free-range houses remain naturally ventilated.

The introduction of even a small amount of added ventilation can have a big impact.

Mike Bowden, managing director at Bowden & Knights, said: “Stagnant, humid air that’s lacking in fresh oxygen can cause issues for both birds and those working on a farm. The main way of tackling this is to get air moving throughout a shed. In naturally ventilated buildings this means opening the vents, but that then brings its own issues, as you immediately become exposed to the outside environment.

“Ideally, free-range chickens should be housed at approximately 21°C all year round. Opening the vents can cause temperatures to drop, with the added issue that the combination of cold and hot air can lead to increased moisture and, if left for long enough, wet litter.

“Likewise, in summer with all the vents open temperatures can still go above maximum recommendations, causing heat stress, lower feed intake, less eggs in layers, and lower weights in free-range broilers.”

According to John Lack, general manager at Hydor, these issues can be overcome by assessing the needs of an individual shed and flock, and suspending recirculatory fans in the roof, creating a better environment for the birds and workers.

Mr Lack said: “The use of recirculatory fans effectively pulls in fresh air from crooks, crannies and holes around the shed, increasing the amount of oxygen available and creating a more pleasant environment for the birds and staff. In winter it means the air can be recirculated without a drop in temperature and in summer, while the temperature remains the same the added air movement cools the birds.”

“Although issues associated with air quality have been brought to a head by the increased amount of time chickens have been required to spend indoors as a result of avian influenza, this small change to free-range sheds could make a big difference to bird and worker welfare, as well as increasing returns at any time of year.”