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Illinois Livestock Trail
Avoiding Heat Stress Problems for Poultry

The Aenvironment@ can be defined as the combination of external conditions (biological and physiological) which affect or have an impact on animals and humans. The external conditions such as weather and climate can affect animal production and physiological responses, however, with poultry the environment usually are those external conditions which are found in the birds microenvironment. These are factors such as nutrition, water, air, temperature, humidity, light, disease, social, sound and wastes. Poultry producers try to control these factors, so that the bird can maintain normal physiological functions and produce meat or eggs at its maximum rate.

Perhaps the most important physiological response of poultry to the environment is the constant maintenance of a homeothermic state (constant body temperature) during exposure to extreme ambient temperatures. During exposure to hot ambient temperatures, poultry have a difficult problem keeping themselves cool and maintaining homeothermic body temperature. Since birds do not sweat, they must rely on evaporative cooling (panting) to keep themselves cool. This increased rate of panting produces what is called respiratory alkalosis of the blood. This physiological response is characterized by an increase in blood pH (more basic), along with a decrease in blood CO2 concentration. This upsets the blood acid-base balance and produces a decrease in blood calcium and bicarbonate which are necessary for the production of strong egg shells. Thus, the ultimate problem is a production of thin-shelled eggs produced by laying hens. As for growing birds, heat stress affects them by depressing weight gain mainly because feed intake is depressed.

In our laboratory, we have conducted several studies in which we have developed a system that is designed to replenish the CO2 lost in the blood of poultry (laying hens) when they are exposed to high temperatures and are panting. This system provides the bird with a constant source of carbonated drinking water. Previous results in our laboratory have shown that egg shell quality could be improved for layers exposed to high environmental temperatures.

In addition to our work with carbonated drinking water, we have explored another avenue of heat stress relief for poultry. Another means of losing body heat in poultry subjected to heat stress temperatures is dissipation of heat through conductive heat loss via the foot pad area. Physiologically speaking, the bird reacts to high temperatures by shunting blood towards the skin surfaces to dissipate heat. Therefore, we hypothesized that if there was a system to remove heat from the birds skin this would effectively help keep the birds body temperature normal. Therefore, we devised a system that allows for conductive heat transfer for broilers subjected to high environmental temperatures. The system is designed to remove body heat by allowing the birds to stand on a water-cooled floor perch, and the perch acts as a heat sink to remove heat. The results showed that final body weight and total body weight gain were improved for broilers exposed to heat stress temperatures for 4 wk and provided with a water-cooled roost.

In summary, physiological responses of poultry to the environment vary tremendously depending on what type of environmental stressor is imposed. The research which we have conducted on ways of alleviating negative effects of heat stress have merit in the commercial poultry industry. Aside from this research, there are some basic practices which a poultry complex manager must follow in order to control in-house air temperatures. The following items should be closely monitored:

1. Make sure fans operate effectively.

2. Make sure fans and air inlets are kept clean.

3. Inspect and/or replace fan drive belts when necessary.

4. Make sure thermostats and static pressure monitors are operating effectively.

5. Provide clear cool water at all times.

6. Don=t overcrowd layers in cages or boilers in a house.

The above list is only a partial list for poultry producers to follow. Following these and many other items will help reduce the devastating effects of heat stress on poultry production performance.

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