Hot weather can have a severe impact on poultry performance. Production efficiency can be affected long before the temperature reaches a level at which survival becomes a concern. Heat stress begins when the 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 its body to dissipate excess heat. Even before the bird reaches this point, anything that you do to help birds remain comfortable will help maintain optimum growth rates, hatchability, egg size, egg shell quality, and egg production.
Heat Stress and Ambient Temperature
|55° to 75°F
||Thermal neutral zone. The temperature range in which the bird does not need to alter its basic metabolic rate or behavior to maintain its body temperature.
|65° to 75°F
||Ideal temperature range.
|75° to 85°F
||A slight reduction in feed consumption can be expected, but if nutrient intake is adequate, production efficiency is good. Egg size may be reduced and shell quality may suffer as temperatures reach the top of this range.
|85° to 90°F
||Feed consumption falls further. Weight gains are lower. Egg size and shell quality deteriorate. Egg production usually suffers. Cooling procedures should be started before this temperature range is reached.
|90° to 95°F
||Feed consumption continues to drop. There is some danger of heat prostration among layers, especially the heavier birds and those in full production. At these temperatures, cooling procedures must be carried out.
|95° to 100°F
||Heat prostration is probable. Emergency measures may be needed. Egg production and feed consumption are severely reduced. Water consumption is very high.
||Emergency measures are needed to cool birds. Survival is the concern at these temperatures.
Temperature Effects on Broiler
|What You See
|Slightly Cool (below optimum)
- Birds tend to huddle together, and spend more time sitting down.
- Feed consumption goes up.
- As temperature drops, more and more birds will “fluff up” their feathers to increase their insulating value, so the birds appear larger.
- The birds are doing what they can to conserve body heat, and at the same time eating more to gain more heat energy from their feed. Since more of the feed energy has to go into keeping themselves warm and less into weight gain, performance is hurt.
|Slightly Warm (just above optimum)
- Birds tend to stay apart more, except they will migrate to cooler and/or higher airflow areas.
- Birds hold feathers closer to the body to reduce their insulating value, and droop or lift their wings to get more air cooling.
- They try to cool their wattles in cups or drinker troughs, and tend to lay flat on the litter if it is cooler than they are.
- They increase water intake, and eat less during the hot part of the day.
- Some of the birds begin panting as temperature rises above optimum, and more and more start panting if temperature continues to rise.
- Birds are doing what they can to increase the rate of heat loss from their bodies. Their circulation changes to pump more blood through legs, wings, comb, and wattles, carrying internal body heat to be dissipated from the extremities.
- Panting cools by evaporating moisture from the respiratory passages; it takes a lot of energy and is a clear sign a bird’s internal core temperature is rising too high. As temperatures rise, birds begin to eat less to avoid the resulting heat load from their feed energy. Performance is hurt both by the drop in feed intake and the birds’ over-temperature defense mechanisms.
- Panting becomes more intense, and many, most or all birds are panting.
- Normally pink skin areas turn a dark red as more of the blood circulation is shifted to extremities and the surface of the body to dissipate heat.
- Feed consumption drops even more, or stops entirely.
- Intense panting and the darkened skin are signs of heat stress, which means birds are unable to get rid of internal heat build-up and their internal core temperatures are rising too high. If high temperature conditions continue, performance is seriously hurt and mortalities increase.
Top temperature points to keep in mind
- Top returns come from keeping temperatures consistently within the birds’optimum performance comfort zone, and maintaining temperature uniformity throughout the house.
- During tunnel ventilation, wind-chill means the temperature the birds feel is not the same as the thermometer reading. The wind-chill effect is more pronounced for younger birds.
- House management and maintenance are essential for keeping birds in their top-performance comfort zone. One example: In hot weather, failing to clean fans and shutters can have the same effect on the birds as turning off two tunnel fans.
Methods of Heat Loss
During the summer months, it becomes critical for the birds to dissipate body heat to the surrounding environment. Poultry do not sweat and therefore must dissipate heat in other ways to maintain their body temperature at approximately 105°F. Body heat is dissipated to the surrounding environment through radiation, conduction, convection, and evaporation. The first three avenues are known as sensible heat loss; these methods are effective when the environmental temperature is below or within the thermal neutral zone of the bird (55° to 75°F).
The proportion of heat lost through radiation, conduction, and convection depends upon the temperature difference between the bird and its environment. The bird loses heat from surfaces such as wattles, shanks, and unfeathered areas under wings. To maintain body temperature by sensible heat loss, the bird does not need to drastically alter its normal behavioral patterns, feed intake, or metabolism.
The purpose of poultry house ventilation is to maintain a high enough air velocity or a low enough temperature in the house that the birds can maintain body temperature by sensible heat loss. Once the environmental temperature reaches approximately 77°F, the method of heat loss begins shifting from sensible to evaporative heat loss as shown in Figure 1. Dissipation of body heat by the evaporative process requires the bird to expend energy by panting (hyperventilation), which begins to occur at about 80°F.
source: ces.ncsu.edu, aces.edu