Heat Stress

Many producers have had a catastrophic loss associated with heat stress at some point.

The more insidious problem with heat stress, though, is the decreased gain and loss in egg production. According to Purswell et al., heavy broilers grown to 63 days were approximately 700 grams lighter when grown in a 26°C humidex compared with 15°.1 Even at 20°C, birds were nearly 400g lighter – and these changes were all due to severely impacted feed consumption levels.

At 26°C, 1100g less feed was consumed, while at 20°, 250g less was consumed compared to 15°. This paints the picture that increased panting causes feed conversion rates to skyrocket to over 4.00 on birds that are typically performing in the 2.05-2.15 range, although at 20°, values were approximately 3.00.

In a study by Feizi et al. in 2012, layers exposed to temperatures 5°C above recommendations lost 50 grams of body weight and declined nine per cent in egg production over 6 weeks.2 These differences illustrate the declines in all types of poultry efficiencies when birds are subject to heat stress.

Tunnel ventilation can be a great way to use wind chill to accentuate the effect of exchanging air from the building. In addition, wind chill can add as much as 6°C in additional cooling over conventional cross-ventilation, based on a wind speed of 500 feet per minute versus speeds typically under 100. These are critical degrees, and also can benefit the birds greatly when other cooling methods are added in extreme heat and humidity.

There are two options though: humidifying the air and sprinkling to cool birds.

The third option is the use of cooling pads, but due to water quality, water consumption and expense of installation, it is not a practical one. In Canada we only require auxiliary cooling for a few weeks every year, unlike the Southern United States and other sub-tropical and tropical countries. Cooling pads are waffled paper or plastic materials, usually about six inches thick. Air passes through the pad as water flows down the pad, adding humidity to the air, increasing its heat carrying capacity and therefore lowering the sensible temperature of the air.

Fogging and Misting
Fogging and misting are popular in Canada. However, adding humidity to the air by using high-pressure foggers can increase the heat carrying capacity of the air, indirectly cooling the birds by reducing the overall temperature of the barn.

At 32°C, with 60 per cent humidity – a maximum of 6-7°C of cooling can be attained. The maximum perceived cooling would actually be just over 3°.

The other problem with fogging is the need for continual maintenance, especially when water conditioning is not ideal, and wetness under the nozzles due to leaking between uses. Cake can also form because increases in air humidity result in increases in litter moisture, and humidified dust will stick to equipment and walls.

Sprinkling
Sprinkling is another alternative cooling method in which a light spray of large water droplets stimulates the birds to stand. It is used as the only auxiliary cooling method in some parts of Canada, and in many and tropical areas of the world, it is used as an additional or primary cooling method in the evening when temperatures are still high, but humidity goes through the roof. Many producers would say that it is not the highest, driest temperatures of the afternoon that cause mortality, but the high and moist temperatures in the evening that cause problems. In a study by Liang et al., humidity in barns cooled with sprinklers had, on average, 20 per cent lower humidity levels.3 This equates to about an 8°C difference due to humidity, while the sprinkler barns were 2-3°C higher. This is a net of 5° in perceived temperature decrease compared to cooling pads or fogged barns. Some other benefits to this method are that birds tend to feed and drink when stimulated, helping to maintain daily gains, and dust levels decrease dramatically, resulting in cleaner barns.

Litter will cake less, and sprinklers generally run at well pressure and have check valves to prevent leaking between cycles.

References

1. Purswell, J.P. et al. (2012). Effect of Temperature-Humidity Index on Live Performance in Broiler Chickens Grown from 49 to 63 Days of Age. Presented at the Ninth International Livestock Environment Symposium, Valencia, Spain, July 2012.
2. Feizi, A. et al. (2012). Effects of Heat Stress (HS) on Production of Hy-Line Layers. Research Journal of Biological Sciences. 7(5): 206-208.
3. Liang, Y. et al. (2012). Sprinklers Cool Birds and Conserve Water. University of Arkansas, Division of Agriculture: Research and Extension. Fact Sheet (FSA1073).