Hot weather can have a severe impact on poultry performance. Poultry producers should realize that high temperatures can affect production efficiency long before survival becomes a concern. Heat stress begins when ambient temperature climbs above 80°F., and is readily apparent above 85°F.

When a bird begins to pant, physiological changes have already started within a bird's body to dissipate excess heat. At this point, anything that you do to help birds remain comfortable will help maintain optimum growth rates, hatchability, egg size, egg shell quality, and/or egg production.

General Hot Weather Management

A grass cover will reduce the reflection of sunlight into a poultry house. Vegetation should be kept trimmed so that air movement is not blocked. Shade trees need to be located where they do not restrict air movement. Fans should be routinely maintained. Maintenance should include cleaning the fan and keeping pulleys and belts in good condition and properly adjusted. Poultry netting on sidewall or air inlets often will pick up enough dust to restrict air movement and should be cleaned on a regular schedule.

Keeping a reliable, clean and cool source of water in front of poultry is essential for birds to cope with high environmental temperatures. Placement of water pipes near the ceiling should be avoided. Draining a warm water line will allow cooler water to reach the waterer. Poultry operations should have a second well or access to an emergency source of water in case of failure of the primary water source.

Another factor which affects heat gain of a house is the condition of the roof surface. A shiny roof surface can reflect twice as much solar radiation as a rusty or dark metal roof. Roof surfaces should be kept free of dust and rust. Roof reflectivity can be increased by cleaning and painting with a metallic zinc paint, or by installing an aluminum roof. These practices are particularly effective for buildings that are under-insulated.

Equipment and Ventilation Techniques Used to Reduce Heat Stress

During the summer months when the temperature and humidity are high, proper poultry house ventilation is vital to insure the necessary removal of heat and the continued productivity of the flock. There are a number of components of poultry house ventilation systems.

These include curtains, fans, fogging nozzles, evaporative cooling pads, timers, static pressure controllers and thermostats. Most ventilation systems can provide an adequate in-house environment when properly managed. If the system design and management fails to satisfy the flock's ventilation needs, stale and contaminated air can build up in the poultry house. Stale air and contaminants, including ammonia, moisture, carbon dioxide, carbon monoxide, and dust, can result in stress and depressed performance. Stress may impair the immune system and increase susceptibility to disease problems. To reduce stale air and contaminant problems, the producer must control air temperature, air speed, and relative humidity through ventilation management.

Natural Ventilation

Curtain-sided houses rely extensively on natural air movement. These houses work best when they are located away from obstructions such as other buildings or trees which block the natural air currents. To escape from total reliance on natural air movement, many producers have added circulation fans in curtain houses to increase air movement and body heat loss from the birds. Fans should be spaced to maintain air movement between fans and turbulent air movement around birds.

Fans should be spaced about 25 to 30 feet between fans in curtain layer houses, and 40 to 50 feet in broiler houses, (depending on fan size). Circulation fans should be controlled by thermostats turning on at about 85°F.(or lower in hot weather) and off when temperatures drop below the setpoint (85o F), to save energy. During periods of extended hot weather it would be advantageous to allow the circulation fans to continue running through the cool hours of the evening by turning thermostats down to 75o F or even lower. This will lower in-house temperatures faster, providing the hens with a cooler environment in which to dissipate stored body heat.

Foggers reduce air temperature in the house on hot days (92-95oF) with low humidity levels, especially during mid-day when humidity levels are lowest and temperature is highest. This is accomplished by injecting fine water particles into a warm environment. As the water vaporizes, heat in the environment is used, which in turn lowers the air temperature. When foggers are used, they should be operated on an intermittent basis or designed to avoid excessive water flow into the environment. If water flow through the foggers is excessive, humidity levels may increase to the point where bird evaporative heat loss is prevented. In addition, wet litter from excessive fogging can lead to performance and health problems. The appropriate water flow rate and timer settings will depend on the method of ventilation, ventilation rate, bird size, and outside conditions. Fogging systems in naturally ventilated houses are typically designed to provide 50 - 100 gal./hour of water flow.

Forced Ventilation

Forced ventilation systems move air entirely by fans in the building walls; this type of ventilation is also referred to as "controlled environment". Power ventilated houses can provide good, uniform air flow patterns under hot summer conditions by maintaining correct static pressure and avoiding air flow obstructions.

Determination of how much air should be moved through the building is very important. This can be accomplished in two ways. A "rule of thumb" for calculating the minimum volume of air required per pound of body weight is given in Table 3 (not shown). The values in Table 3 can be used to determine the total fan capacity required in the house. However, the rates shown are minimum estimates, and worst case scenarios must be anticipated. For example, fan efficiency is greatly reduced if they are allowed to become excessively dirty thereby reducing the CFM pulled through the building. A second method is to calculate the interior volume of the house. Once this is done, a summer ventilation rate of one air exchange per minute can be calculated.

Negative pressure systems are designed to operate best with a static pressure of .03 to .08 in. of water. This pressure allows the air to travel from the air inlets along the ceiling, until it meets the stream from inlets on the opposite side of the house, and drops in the center of the house, creating air turbulence. The air then travels toward the exhaust. If the pressure is too low, the velocity of the air is reduced as it enters the building, resulting in the air flow dropping to floor level and traveling toward the exhaust fan.

Conversely, if the static pressure is greater than .08 in. of water, the velocity of the inlet air is increased, but the volume of air moved is restricted and fan efficiency is reduced due to back pressure on the fan blades. This can result in pockets of stale air within the house with little or no velocity, which is detrimental in summer conditions. Dead air zones must be avoided by proper inlet placement and system management. The location and orientation of the inlets is the single most important factor influencing the air flow pattern inside the building.

Tunnel Ventilation

A new arrangement of ventilating poultry houses in the summer is tunnel ventilation. Simply put, this method involves moving air along the building axis from inlets to exhaust fans, which provides high air velocities. This in turn increases convective heat loss, reducing the effective temperature that the bird is feeling. Figure 2 (not shown) shows the effective temperature (wind chill) the bird is feeling at a given environmental temperature and air velocity. Research by Drury (1966), showed that most of the benefits of tunnel ventilation occur at an air velocity of 350 ft./min. This should be considered the minimum air velocity for most house designs. Tunnel ventilation systems do not operate on a static pressure. In fact, they work best when there is no pressure difference between inlets and the fans.

Evaporative Cooling with Power Ventilation

Both fogging nozzles and evaporative cooling pads are additional options which can be used in combination with power and especially tunnel ventilation. Evaporative cooling (cooling air by evaporating water) uses heat from the air to vaporize water. This method increases humidity but lowers air temperatures in poultry houses. Evaporative cooling can be effective in North Carolina during the hottest part of most days since that is when humidity is lowest. On rare occasions the humidity will remain high the entire day or immediately before or after a storm; evaporative cooling will be ineffective and should not be used during such conditions.

Evaporative cooling pads utilize the same method of cooling as foggers, except that air is cooled as it enters the house. This reduces the problem of wet litter and allows evaporative cooling pads to be used on a continuous basis. Aspen Fiber and Corrugated Cellulose are two materials widely used as cooling pads and require scheduled maintenance to insure a long life.

First, the pads need to dry out once each day of use. This is done in the early morning hours when the outside temperatures are lower. The drying allows the adhesive holding the pad together to maintain its integrity and also helps reduce the buildup of algae. To reduce the growth of algae, an algicide can be used in the water for the cooling pads. The algicides Calcium Hypochlorite, Ethylene Dichloride, and Ammonium Chloride can be administered at a rate of 6 oz./ 1000 gal. of water, applied once each week. In addition, the pads should be washed on a monthly basis to remove dust and sediment.

The entire system should also be flushed on a monthly basis to remove the buildup of mineral salts and dirt which accumulates in the pipes and reservoir. Evaporative pads constructed of aspen or cellulose ranging in thickness from 2 to 6 inches are being used in the industry in conjunction with power ventilation systems. These pads evaporate water at a rate up to 100 gal./min. (gpm)/100 ft2 of pad on a hot, dry day and 200 gal./min.(gpm)/100 ft2 of pad using tunnel ventilation on the same day. Fogging systems have also been used successfully in environmentally controlled poultry houses. Fogging systems which provide a reliable fine mist and have water filters (to keep nozzles from clogging), and a positive shutoff to prevent dripping can provide successful cooling without causing wet litter.

The water pressure should be at least 100 pounds per square inch (psi)(preferably 200 psi) to achieve a fine mist. The quantity of water going through the fogging system and the number and placement of the nozzles are critical design considerations. A total flow rate of up to 1 gal./h per 1000 cfm of ventilation rate can be used in tunnel ventilated houses. The design of the fogging system is critical for tunnel ventilated houses. Cross lines of nozzles, which provide a "curtain" of fog across the house at various intervals, are fairly effective.

Nozzles or lines of nozzles should be located closer together near the air inlets, then have increased spacings further along the house, ending 60 ft from the exhaust fans. Tunnel ventilated houses can use substantially more fogging capacity (50 - 100 % more) than naturally ventilated houses, due to the guaranteed air movement being able to carry the mist.

The value of a summer ventilation system should not be underestimated. If the summer ventilation system is operating properly, it can improve litter quality, reduce dust levels, and improve the flock's rate of gain or production levels. The key to operating any ventilation system is understanding how it works. In addition, a good maintenance program of cleaning, adjusting, and monitoring controls for the curtains or inlets will maintain system efficiency. Fans in any ventilation system should be frequently cleaned and lubricated, and fan belts should be periodically adjusted, especially during times of heaviest use. If foggers are used, they should be serviced periodically to insure a uniform fine particle fog is being generated. If questions arise concerning the operation of your ventilation system, consult your flock supervisor.

July 2006