Managing Heat Stress in Poultry Amy E. Halls, Monogastric Nutritionist Shur-Gain, Nutreco Canada Inc. Heat stress has several serious and economical effects on poultry. In broilers and turkeys, it can cause reduced growth rate, decreased feed intake and poor feed conversion. Laying birds experience a drop in egg production, poor egg weight and reduced eggshell quality. For all types of poultry, heat stress can also cause increased mortality. It is important to recognize and manage heat stress in poultry in two areas. 1. Reduce the amount of heat birds are exposed to. 2. Change management and feeding to keep birds cool. The five natural methods by which birds control excess body heat are: radiation, conduction, convection, excretion and water evaporation. Radiation: Transfer of heat by electromagnetic means is an important method of heat control. Heat will radiate from the bird s warmer body to a cooler surface, such as air, without the use of a medium (surface). During hot weather birds will raise their wings to allow heat to radiate from poorly feathered areas, such as under the wings. Caged leghorns survive well in hot weather because they are not in contact with floor litter. Conduction: Conduction involves the transfer of heat from a warm surface to a cooler surface. Heat stressed birds will try to cool their bodies down by touching water pipes or digging into litter to come into contact with a cool floor. Caged layers will touch the sides of the cage. Convection: Moving air over birds is the most effective way to reduce heat stress. If the air is not moving quick enough, heat will begin to build up around the birds, which will increase heat stress. Proper ventilation is the key to keeping birds cool in hot weather. Excretion: Excretion is another method birds use to keep cool. Birds normally double their water intake during hot weather and excrete heat through urine and wet feces. Thus, it is very important to ensure barns have enough drinkers that will dispense sufficient volume of water, clean water filters, and well-adjusted pressure regulators to maximize water output during hot weather. 1
Water Evaporation: Water evaporation occurs on the surface of the skin and from the respiratory tract. The nasal cavity is a heat exchanger and therefore helps rid the body of excess heat through evaporative cooling. Panting is the most obvious clinical sign of heat stress in poultry. What Happens During Heat Stress? Turkeys, broilers and layers perform well in comfortable summer temperatures between 70 80 o F (21-27 o C). When ambient (surrounding) temperatures rise above 80 o F, feed intake, growth and production are affected. Heat exhaustion and death will occur when temperatures exceed 90 o F (32 o C). High humidity and high ambient temperatures are extremely stressful for birds. If the amount of heat produced by a bird is greater that the amount it loses, the bird s body temperature will increase. During hot weather birds will limit their daytime activity and will reduce feed consumption or stop eating. Feed consumption and digestion increases body temperature, and thus birds will decrease their feed intake to reduce their body heat production. Decreased feed intake will affect bird performance and profitability. Water consumption will also increase in hot weather, which will result in wetter droppings and litter. Reductions in feed intake will cause decreased body weight gain, egg production and lower egg weights in layers. Eggshell quality is also affected in hot weather, but not entirely due to the dietary calcium deficiency resulting from decreased feed intake. As the hen pants to keep cool, excess carbon dioxide is exhaled, which causes the blood to become more alkaline. The alkalinity of the blood reduces its capability of carrying calcium to the reproductive system for shell formation. Increasing dietary calcium will not improve shell quality. In order to keep cool, birds will increase their respiration rate as much as ten times the normal rate and indulge in throat flutters or panting. Throat fluttering allows the evaporation of heat by moving air in and out of the throat area without actually entering the lungs. This method is very efficient on hot dry days, but it is not very helpful during hot humid weather because evaporation is more difficult. Older, heavier birds are less able to manage heat stress. Due to the lower body surface area per kilogram of body weight, older birds produce more internal heat and are less able to cool down by convection and evaporation. Older birds have more feathering and hence more insulation, which also makes it more difficult to get rid of body heat. In addition, as birds become larger there is less space between individuals in the poultry house, which traps more heat between birds and significantly increases the temperature at the floor level. Thus, air movement is an important method of keeping older flocks cool. 2
How to Control Heat Accumulation in Poultry The most important measure to combat hot weather is to reduce the amount of heat accumulation in poultry. The sooner a heat stressed bird can bring its body temperature back to normal, the quicker it will get back on feed and the more likely performance will not suffer. Ventilation, bird density and nutrition are a few areas that play a role in controlling heat accumulation. Stocking Density The higher the bird density in a barn, the more heat produced. Birds in high density stocked barns tend to absorb each other s radiant heat load, which makes heat management more difficult for the birds. Reducing the bird density in the summer will give more floor space per bird and allow more heat to escape from underneath their bodies and from the litter. Also, less crowded barns allow birds to move more freely to nearby water lines. Table 1. Minimum floor area recommendations for typical broiler weight categories. Evaporative Cooling Mature Bird Weight Recommended Minimum Density Kg m 2 /Bird Kg/m 2 1.7 0.06 27.80 2.0 0.07 27.80 2.2 0.08 27.80 2.5 0.09 27.80 3.5 0.13 27.80 Sprinklers are commonly found in turkey barns for evaporative cooling, which are used when temperatures are more than 79-86 o F (26-30 o C) and the barn air is very dry. Too much water can actually increase the humidity of the barn to dangerous levels. Remember, high temperatures and high humidity make heat dissipation by evaporation very difficult. Death due to heat exhaustion will occur more quickly if both temperature and humidity are high. Nutrition Panting is accompanied by an increase in water loss so more water has to be consumed by birds during hot, dry weather in order to prevent dehydration. Drinking water cooler than body temperature will absorb body heat, which will help with cooling the bird. Adding an electrolyte to the drinking water will replenish vital nutrients that will help balance blood ph levels. Offering a night-time feeding program will encourage birds to eat during cooler periods and help maintain their performance during hot weather. 3
Ventilation Proper ventilation is crucial for heat stress management. A good ventilation system performs the following: 1. Removes moisture laden air from the poultry house. 2. Brings in an equal amount of fresh outside air. 3. Directs incoming air to all areas equally. 4. Keeps inside air moving to flush hot, humid air from between the birds. In order to adequately handle a heat wave, the ventilation system should have the following: 1. A static pressure monitor to show the amount of suction or negative air pressure exerted on the building by the exhaust fans. Exhaust fan capacity is the total fan capacities of all exhaust fans in the poultry house. Fan capacities can be obtained from the suppliers and manufacturers. Note. All fans should be clean as dust build-up will reduce the fan s efficiency. 2. Adjustable air-inlet baffles that can give an even flow of fresh air to all areas without restricting the fans. 3. Total exhaust fan capacity of 3.5 litres per second (L/s) per laying hen (7 cubic feet per minute (cfm) per laying hen). 4. Total intake opening area of 0.18 m 2 per 500 L/s (2 square feet/1,000 cfm). Ventilation Air Intake In order to provide a uniform supply of fresh air, air intakes should be continuous along the length of poultry barns. For layers, one inlet should be provided for every two to three cage rows. Layer houses with more than three cage rows should have inlets on both sides. If the air inlet width is not the correct size for the number of birds housed the fresh airflow into the barn will be restricted when the maximum ventilation is required. Table 2 gives the required width openings for continuous air inlets. Table 2. Required width of continuous air intake openings (P. Hunton et al., 2000). # Birds/m of Intake Length Metric Required Intake Width (mm) # Birds/ft. of Intake Length Imperial Required Intake Width (in.) 80 100 24 4 120 150 36 6 160 200 48 8 200 250 60 10 240 300 72 12 280 350 84 14 320 400 96 16 4
The air inlet baffle opening should be adjusted to create a static pressure (or room vacuum) that will provide the best possible air flow pattern in the barn. All rooms should be equipped with a static pressure gauge that will help you obtain the correct settings. For summer airflow a static air pressure between 0.04 and 0.06 inches of water is required. Static levels higher than 0.06 inches will prevent the airflow from reaching the birds at floor level and instead will force most of the air to travel across the room near the ceiling. This is of little benefit to the birds. Ventilation Air Exchange Rate Sufficient air exchange is important during hot weather. For the majority of poultry barns, this means the air within the barn should be exchanged every 60 seconds. Higher ceilings actually trap hot air within the barn, adding to the heat stress of chickens. Ventilation rates can also be based on bird weight, as indicated in Table 3. As a guideline, the minimum ventilation rate during the summer should fall between 7 and 10 cfm (cubic feet per minute) per bird. These rates will result in an air exchange every minute. If the barn ceilings are greater than the standard 8-foot ceilings, the rates should be proportionately increased to ensure that all heat is continuously removed. Table 3. Ventilation rates according to bird weight (Huffman et al., 2000). Bird Weight Category (kg) Alarm Systems and Emergency Equipment Minimum Summer Ventilation (cfm/bird) 1.7 7.0 2.0 7.5 2.2 8.0 2.5 8.5 3.5 10.0 Equipment alarms to warn poultry producers of ventilation system failure are not only common features of modern ventilation systems, but they are also mandatory when poultry welfare depends on powered ventilation. The main consequence of failure of the primary ventilation system is a temperature rise with risk of heat stress and death. Death can easily occur within a few hours after equipment has malfunctioned during hot weather. All poultry barns should be equipped with a generator in case a power outage occurs during hot or cold weather. 5