Canadian Poultry Magazine

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Coping with heat stress

May 2003


October 2, 2012
By Jim Knisley


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Ontario lost a large number of birds last summer to heat, Harry Huffman, an agricultural engineer who specializes in ventilation, told about 60 broiler producers at a seminar in Holmesville, Ont. sponsored by the Ontario Ministry of Agriculture and Food.

Southern Ontario had 46 days with temperatures over 30 degrees C, 13 days over 34 degrees and eight days over 35 degrees.

While there was little precipitation last summer there were a number of days with very high humidity, which increases the heat stress, he said.

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“Heat stress is most severe when high temperatures are coupled with high humidity,” he said.

Environment Canada has developed a formula that combines the two factors to create a Humidex reading. These readings reflect the comfort level for people.

While no Humidex reading has been done for livestock, Huffman said, it’s safe to assume that animals will have somewhat similar degrees of discomfort with heat stress.

Humidex comfort levels on the chart are as follows: 29 or lower, no discomfort; 30 to 39, some discomfort; 40 to 45, great discomfort, avoid exertion; above 45, dangerous; and above 54, imminent heat stroke.

As long as the humidex is below 54, growers can do a number of things to reduce the severity of heat stress. Above that level, “it is quite likely some bird losses will occur regardless of housing management,” he said.

The first thing is not to overcrowd summer flocks.

Second, acclimatize the birds to possible heat stress at four weeks of age by allowing the barn temperature to rise for several hours. Research shows that short bouts of heat stress will help the birds survive future heat stress periods.

Third, increase the light level in the pen prior to operating large-diameter fans or opening tunnel ventilation doors. This will reduce the fear reaction and subsequent flight from the bright areas. This type of flight reaction has caused piling near the centre of the barn and suffocation.

Fourth, exhaust sufficient air in hot weather. Try to keep the barn within two degrees of the outside temperature and aim for a complete air change every minute.

Fifth, ensure that the air inlet has sufficient capacity to handle the fresh airflow. There should be at least 1.5 square feet of inlet opening for each 1,000 CFM of fan capacity and some insurance companies insist on two square feet for heat prostration coverage.

Sixth, verify proper air intake velocity with a static pressure gauge. In order to have good air movement it is important to have lower static pressure in summer. The usual range for summer, he said, is .03 to .06 inches while in cold weather the range will be .05 to .08 inches static pressure.

Seventh, if the static pressure is too high increase the fresh air openings. Ideally, this will be done by increasing the air inlet opening of the addition of more air inlets to enhance the airflow over the birds. Doors can be used, he advised, if they are only opened to the extent necessary to bring the static pressure down to the correct range. Opening too many doors will eliminate the vacuum and airflow will be less than required everywhere except directly in front of the openings.

Eighth, make sure the air is moving across the barn at bird level. This air movement is required to remove the heat from the bird as quickly as possible. Moving air at a reasonable speed around the birds’ heads and necks has the potential to reduce the perceived temperature by one to three degrees Celsius.

There are a number of ways to increase air movement at bird level, he said.

These include: a deflector board for a typical side air inlet; a new double side air inlet system; a second air inlet lower on the side wall; a second air inlet on the opposite side of the barn; tunnel ventilation; tunnel ventilation baffles to increase air speed; and internal air circulation fans.

Ninth, make sure the birds get plenty of cool water. Water consumption should double during hot weather.

Tenth, slowly walk the birds during periods of heat stress. This promotes air movement and releases the heat trapped under the birds, Huffman said. It also encourages the birds to move to the drinkers and allows you to more closely monitor the birds. However any bird activity generates more body heat and can increase heat stress. Therefore, this walking exercise may be best if done in the morning when it is usually cooler.

Eleventh, ensure that the attic is properly insulated and ventilated.

Twelve, any colour other than white will absorb significant solar heat. There can be significant attic heat reduction if the roof is painted white. In addition, there are now ceramic paints or coatings available, in a variety of colours that will reduce solar heating.

Thirteenth, if possible have the air inlet on the shady side of the building.

Fourteenth, talk to your feed company representative and veterinarian about feed withdrawal practices during periods of heat stress.

Fifteen, consider some form of evaporative cooling. Adding water vapour to the air is an excellent way to bring down air temperature, he said. Depending on the humidity levels evaporative cooling can reduce air temperatures anywhere from one to six degrees because the water vapour absorbs heat.

The impact can be dramatic. For example (referring to the Humidex chart), it can be seen that if one could bring the temperature down from 34 degrees to 30 degrees the Humidex would be in the safe zone even if the humidity rose from 80 to 85 per cent. Even at 90 per cent humidity the Humidex is 45.6 compared with 52 at 80 per cent humidity.

In summary, Huffman said there are a number of things that can be done to help your birds survive the heat, but they require planning and may involve some spending.

“Therefore, give the various options some thought over the winter and have your improvements in place prior to next summer’s heat wave,” he said.  


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