COOL MANAGEMENT FOR HOT CHICKENS

Every summer, hot weather takes a heavy toll on poultry production in the southeastern U.S. By understanding the physiological and behavioral mechanisms that are available to birds to combat heat stress, we can be more effective at managing poultry during periods of high temperature and at minimizing losses due to mortality and morbidity.

Birds, like mammals, are homeothermic. They produce heat to maintain a relatively constant body temperature. A five-pound broiler will produce over 50 BTUs of heat per hour which means it must get rid of over 50 BTUs per hour to maintain constant body temperature. It is scary to realize that 20,000 five-pound birds in a typical broiler house produce one million BTUs of heat per hour. Maintaining a constant body temperature is not a problem when air temperature is at least 10-15 degrees less than body temperature. Normally, the chicken's body temperature is 104-107^oF, but will fluctuate somewhat depending upon the temperature of its environment. There is a lot of margin for error on the low side; in cold weather a chicken's body temperature can drop as low as 73^oF before death occurs. However, there is much less flexibility on the high side. The upper lethal limit on body temperature is 113-117^oF. The chicken must be able to get rid of excess body heat quickly or it is in trouble.

Although birds and mammals are homeothermic, birds have a number of thermoregulation characteristics different from mammals. The most obvious is feathers. Feathers are great insulation which is good for cold weather but bad for hot weather. Feathers tend to hold heat in and not let it escape easily from the chicken's body. Another difference is that birds have no sweat glands. Most mammals perspire when they are hot, and evaporation of this perspiration from their skin is extremely effective in reducing body temperature. Nevertheless, birds have a couple of special features that do help them during hot weather. Their relatively high body temperature makes it easier for them to lose heat to the air around them. Also the bird's respiratory system is very effective at cooling. The air sacs of the bird allow inhaled air (which is usually cooler than body temperature) to reach deep into the abdominal cavity, and of course when the bird exhales, heat is removed from its body. The bird also has a panting mechanism (gular flutter) that it uses during hot weather to evaporate water from its throat and reduce its body temperature. Thus panting in birds is analogous to perspiring in mammals and is extremely effective at cooling the bird.

Air movement is critical. A bird can only give off heat to its environment if the temperature of that environment is cooler than the bird. If heat produced by the birds is not moved away from them and out of the poultry house quickly, it will be more difficult for them to avoid heat stress. The best ventilation systems provide at least one air exchange per minute. Also, it is critically important to continue moving air during the cool parts of the day and night. When birds can get relief from the heat at night, they perform much better.

Under normal conditions, chickens can do a good job of cooling themselves with physiological and behavioral mechanisms; however, during sustained periods of high heat and humidity, considerable mortality and morbidity losses can occur. The producer can do a lot to relieve heat stress.

Housing and ventilation equipment are two of the most effective means of reducing heat stress. The modern poultry house provides more ceiling insulation to keep radiant heat out of the house than we have seen in the past. Also, most modern poultry houses provide at least some form of evaporative cooling. The ultimate, but most expensive, poultry houses are equipped with evaporative cooling pads, a tunnel ventilation system, automatic curtain drops in case of power failure, and alarm systems. Other houses are equipped with foggers to provide evaporative cooling. The most important thing a producer can provide to cool birds in any type house is good air movement. Air movement is key because it prevents heat given off by the birds from building up around them. This produces a wind chill and increases the movement of heat away from the birds. A light breeze of four miles per hour (350 feet per minute) reduces the effective temperature sensed by the bird by 10-15 degrees.

Acclimation to heat can be very important in reducing losses during hot weather. Most often it is the sudden heat waves that cause the most damage during the summer. Research at North Carolina State, Oklahoma State and The University of Georgia has shown that birds are able to adjust to heat if they are allowed to become accustomed to it gradually. Recent studies at Virginia Tech have shown that if birds are subjected to a brief heat stress early in life, they are much more capable of withstanding heat stress later in production. There is much we don't understand about how birds acclimate or why early exposure reduces future susceptibility to heat. As more is learned about these mechanisms, we will certainly be better able to reduce heat losses.

Sufficient water is absolutely essential during hot weather. Watering systems must be in peak condition. If nipple drinkers are being used to grow large birds, pressure regulators must be adjusted to supply maximum water. If birds can get water on their combs and wattles, evaporation does much to cool them.

Increasing floor space per bird during hot weather is necessary in houses with marginal ventilation and evaporative cooling systems. Reducing bird numbers reduces the amount of heat produced and the amount of heat the ventilation system must remove from the house. Increasing floor space also increases watering space and availability which aid in reducing heat stress. Nevertheless, research at The University of Georgia has shown that broilers can be grown with excellent results during hot weather at winter densities in properly designed and operated tunnel ventilated, evaporatively cooled houses. These studies also indicated that increasing bird numbers in evaporatively cooled, tunnel houses during the summer months made it possible to economically justify the increased building and operating costs associated with such houses.

It is often asked if broilers should be walked during hot weather. Studies have shown that sitting can reduce heat loss from unfeathered feet and legs of birds by 20-50% compared with standing. On the other hand, the simple act of standing may increase metabolic heat production from 20-40%. In many cases when birds are walked, they will go and drink. For this reason alone, it may be beneficial to walk broilers during hot weather, but do it very slowly and carefully to avoid unnecessary activity in the birds.

Combating summertime heat is probably the greatest challenge for poultry producers. Mortality and decreased production efficiency are constant threats. Listed below are some ideas which you might want to consider during the months ahead to aid your birds in coping with heat stress.