Broiler Management in Warm Climates

Robert A. Swick
American Soybean Association
Singapore

Introduction

Warm temperature and high humidity reduce performance and profitability of broiler production. In temperate climates, healthy broilers growing under comfortable conditions will undergo serious life threatening heat stress when temperatures and humidity are suddenly elevated. Mortality rates as high as 50% are often observed during sudden periods of hot and humid weather. In contrast, birds growing under tropical conditions have constant high daytime temperature and humidity throughout the growout and become acclimated. In this situation, mortality is rarely over 10% unless there is a disease outbreak. The major problem in the tropics is poorer weight gain and feed conversion as compared to the genetic potential. Often this represents a massive loss but is considered "normal" by growers for their climatic situation. Because of increased competition and weakening economic situation, broiler growers and integrators in Southeast Asia have recently begun to invest in insulation, power ventilation and even evaporative cooling for broilers. The purpose of this report is to review the effect of heat and humidity on the physiology of the bird and to discuss cost effective techniques available to maximize profit in warm climates.

Temperature and Humidity

The relationship between temperature and humidity on stress in broilers is depicted in Figure 1. Factors such as age, length of exposure to warm conditions, temperature of drinking water, movement of air, radiant heat load, stocking density, nutrition and others affect the exact temperature and humidity that cause mortality and reduced performance. The effect of high temperature is always much greater when humidity is high.

The normal body temperature of a broiler is about 41.5ºC. Any combination of temperature, humidity and the factors above that act to increase body temperature will cause stress. With an environmental temperature of 37ºC and relative humidity of 55%, body temperature will soar to 45ºC. At 37ºC and 75% relative humidity, body temperature will exceed the lethal maximum of 47ºC and the bird will die. Any condition above normal comfort will reduce performance and profit.

Physiology of Heat Stress

Birds constantly regulate heat loss from the body. Energy and heat flow in broilers is depicted in Figure 2. Blood vessels become dilated in peripheral tissues such as the comb, wattles and legs. These parts will feel warm when the bird needs to lose heat from deep body tissues. Posture will change as wings are held open and away from the body so that heat can be lost from unfeathered areas and to increase surface area. Water consumption will increase as the bird attempts to get cool and flush out heat during excretion. Feed intake decreases to reduce heat production caused by metabolism and activity of eating. Up to 75% of the metabolizable energy consumed by the broiler is converted to heat. This must be lost to the environment. The affect on performance is obvious.

Panting occurs in birds when body heat becomes excessive. This allows heat to be removed by evaporation from the respiratory tract. This is the principal means of regulating body temperature during heat stress. This method becomes limiting as humidity increases as water loses its ability to evaporate. Increased humidity and temperature will cause the respiration rate to increase. The normal respiration rate of 20-30 breaths per minute will increase as high as 150 or more. The length of time a bird can maintain respiration rates over 100-110 per minute is limited to about 6 hours. Respiration rates over 200 per minute are lethal in 30 minutes or less. Figure 3 shows the relationship between respiration rate and time on stress.

While panting provides evaporative cooling, it also results in dehydration and loss of carbon dioxide from blood and tissues. Prolonged panting will cause respiratory alkalosis. The bird responds by excreting potassium and bicarbonate from the kidney, which may result in an acid-base-electrolyte imbalance. This further affects many metabolic processes including nutrient digestion. Overall, profit and performance is lost through poor weight gain and feed conversion and high mortality.

Management Can Improve Profit in Warm Climates

The most effective way to maintain production during warm weather is to keep the birds as cool as possible. Research has shown that each 3ºC increase in house ambient temperature over 33ºC will reduce growth by 0.9% and FCR by 2.1% (North, 1984). Much greater reductions in performance can be expected as temperatures increase further. Figure 4 shows the effect of warm and humid conditions on broiler FCR in the later period of the growout in two experiments in controlled chamber rooms (Swick, 1989: Giesen et al., 1997). In experiment 1. An average house temperature increase of 6.5ºC from 24ºC with no added humidity (30% R.H. maximum) resulted in a 9.6% loss of FCR. In experiment 2, an average temperature increase of 7.5ºC with added humidity added (70% R.H. maximum) resulted in a 31% loss of feed efficiency. Clearly, profit saving would be gained by keeping the birds cool. Figure 5 shows the values of the savings with various feed costs. A house holding 5,000 birds with 5 cycles per year and an average feed cost of US $250 per MT would save between $1,175 and $3,250 per year in reduced feed cost due to improved FCR using measures to keep birds cool.

By considering each of the five method birds use to dissipate heat, one can devise the best and most cost-effective strategies to keep the birds cool.

1. Evaporation - Panting causes water to be evaporated from the respiratory tract which removes heat. An adequate supply of water is necessary. Remove humid air from poultry house.
2. Convection - Cool air moving past the bird will carry body heat. Maximizing natural ventilation and provide fan assisted ventilation.
3. Radiation - Heat will move from warm objects to cooler objects. When the surface of the bird is warmer than its surrounding, heat will move away from the bird and vice versa. Roof insulation and shade are highly effective in keeping the localized air cooler than the bird.
4. Conduction - Heat transfers from the bird to a cooler object by direct contact. Concrete floors with thin litter are effective heat sinks during the warmest part of the day.
5. Excretion - Large amounts of heat leave the body through excretory waste. Ample cool water should be provided.

Water

An adequate supply of water is absolutely essential during hot weather. Watering systems must be in peak condition and management must check and maintain the water system continuously. If nipple drinkers are used, pressure regulators must be adjusted to supply maximum water. Water that gets on combs and wattles will be effective in cooling. Water temperature is important. Water tanks should be located in the shade and /or be insulated to prevent heat gain. This is also true for water supply lines. These should be buried underground and not placed where they are exposed to the sun. The cooler the water, the better the performance. Water consumption may also be encouraged by gently walking through the birds in mid or late morning before maximum temperatures occur. Water-soluble electrolyes may also be useful to increase water consumption and replace minerals lost in excretion.

1. Several simple and cost-effective measures can be taken when constructing new broiler houses.  
2. Dimensions and design - A long and narrow house will provide more ventilation than a square house. A width of 10 to 12 meters should be considered maximum. Many houses in tropical areas are 6 to 8 meters wide. The slope of the roof should be as steep as economically possible with a large ridge vent. This will increase airflow with warm air rising and cooler air taking its place from the outside. Simple considerations for open house designs are given in Figures 6 and 7. The decision to use litter or slats should be based on availability or litter and cost of material and labor for slats. Litter houses are easier to clean and require less maintenance. Natural immunity to coccidiosis is developed at an earlier age with litter. Slatted floor houses provide more airflow but are more difficult to convert to tunnel ventilation.
3. Orientation - The house should be oriented so that afternoon sun shines on the small narrow end of the house. A naturally ventilated house should be placed to take advantage of natural air movements and not placed in narrow valleys. The distance between houses should be as far as possible but certainly not less than 10 -12 meters. Vegetation that blocks airflow should be removed. Tall trees that provide shade will help keep birds cool. 
4. Insulation - An R-value of 4 is recommended for under roof application in open naturally ventilated houses (North, 1984). Less than 4 if power ventilation (fans) will be used. Typical materials would be: dead air space (solid sheet under roof with air space 2.5 cm = R2.3); urethane foam sheets (2.5 cm = R5.00); aluminum and plastic bubble film (1 cm = R2.00); traditional grass or attap leaf roofs (2.5 cm = R1.75). The money saved in feed conversion can be used to calculate the payback of the insulation. Table 1 and figure 4 gives results of two experiments with different temperature and relative humidity and their effect on FCR and feed cost savings with different feed prices.  
5. Roof material - A light color will reflect away heat and result in a cooler house. Roof sprinkler may also be a consideration if water is plentiful and drainage is good. In the long run, insulation is likely to be more cost effective. 
6. Fogging - Many broiler houses in the Southern part of the U.S., where summer temperature and humidity exceeds that of Southeast Asia have found success with automatic thermostatically operated high pressure fogging. High pressure water nozzles are placed inside of the poultry house near fans. The mist evaporates quickly and cools the air temperature that then passes across the birds. When operating correctly, the mist is extremely fine and does not result in buildup of moisture on the litter. The maximum ambient relative humidity for effective fogging would be around 70% during the heat of the day.  
7. Tunnel Ventilation - Tunnel ventilation should never be used when birds are trying to conserve heat when they are young or during cooler temperatures at night. In this system, large operating with separate thermostats are placed at one end of broiler house and operated with the curtains closed except for those at the small end of the house. Fences should be provided inside the house to prevent migration. The method employs a moving a uniform air column across the birds to maximize convection of heat. Thermostats should begin to operate fans at 29ºC and continue to turn on fans until air temperature reaches 32ºC (Czarick and Lacy, 1991). Under U.S. conditions, on acreage, broilers typically will be 3 to 5% heavier at processing, have 2 to 3% improved FCR and 20-30% lower mortality.  
8. Evaporative cooling - Cooling pads can be erected on the far end of the tunnel house to provide evaporative cooling. The most effective way to wet the pads is by mist jets. A maximum of 9 liters per hour for every cubic meter per second of exhaust fan capacity should be provided for maximum cooling and minimum moisture buildup in the house.  

Bird Management

Healthy chicks that have not become dehydrated or subjected to heat stress in transit should be started on water for several hours before supplying feed. At 3 to 4 weeks of age the stocking density should be reduced to 8 to 10 birds per square meter (more than 1.2 sq ft per bird) to facilitate convection and heat removal. This can be increased if power ventilation or evaporative cooling is employed.

1. Feed restriction - Feed may be restricted if sudden high temperatures are anticipated. This is often beneficial to prevent mortality as body heat rises 7 to 12% two hours after feeding. In this situation, feed should be preferably removed for a period of 6 hours before the stress begins. This will improve survival but will have a negative affect on performance. Feed restriction is of much less value in acclimated tropical birds that have been reared under constant high daily temperatures.  
2. Particle size, pelleting and density - Birds spend considerable energy consuming feed. Because of this, feeds of high bulk density and high nutrient density are advantageous in warm climates. The rate of nutrient intake per energy spent consuming feed should be as high as economically possible. Dusty mash feed of small particle size is more difficult to consume and more costly to produce and should be avoided. Pellets and crumbles provide the best situation for feed consumption.  
3. Nutrition - The physiology of panting results in loss of carbon dioxide and potassium from the system, which should be replaced. Replacement of 50% of the added salt with an equivalent amount of sodium from sodium bicarbonate is recommended. The use of soybean meal as the sole protein supplement in broiler diets is useful in that it is rich in potassium (2.0%) relative to fishmeal (0.75 – 1.25%) or canola meal (1.25%). Care should be taken to supply a balance of amino acid in the diet to minimize nitrogen excretion. An excess or unbalance of amino acids induces formation of uric acid, which generates heat in the bird. Fat, as an energy source is also useful in that it produces less heat than carbohydrates during metabolism. Full fat soybean meal is and excellent ingredient as it contains 18% high quality fat. Use of phosphate sources that provide more phosphate and less calcium are also be useful in that more limestone and thus carbonate will be present in the feed. A good quality and digestible phosphate source is especially important during hot weather (McCormick, 1981). 
4. Feed Quality - Each 10º C increase in temperature will double the rate of oxidation and mold growth in feed. Humidity and accidental wetting of feed by rain during delivery and storage is also common. Moldy and oxidized feed will reduce performance and decrease resistance to disease. Mold inhibitors based on propionic acid should be used and antioxidants based on ethoxyquin should be used in fat sources, high fat ingredients and vitamin premixes.  
5. Vitamins - Vitamin C (ascorbic acid) a water soluble antioxidant vitamin that is normally produced in adequate quantities by metabolism in broilers. During heat stress this process is limited. Thus stabilized forma of Vitamin C have been found useful under certain situations. Vitamin E at levels above 80 ppm has also been reported to be useful during stress situations.

Conclusion

Broilers are constantly producing heat as they eat and grow. This waste heat needs to be eliminated. Hot and humid weather slows this natural process and reduces performance and profit. Anything that can be done to remove heat in the broiler house will be beneficial. Birds can be kept cool by providing adequate ventilation, ample cool water and prevention of solar radiation into the chicken house and water system. Use of insulation and shade are cost effective and will improve profits. The use of high chick quality, balanced nutrition, lower stocking density, tunnels ventilation and evaporative cooling are also extremely useful.

1. Czarick and Lacy, 1991. Performance of tunnel-ventilated broiler houses with misting nozzles. American Society of Agricultural Engineers Paper 91-4562.  
2. Giesen, A.F., C.D. Knight, F.J. Ivey, H.B. Harlow, J.J. Dibner. 1997. Performing when the heat is on. International Poultry Production.  
3. North, M.O. 1984. Poultry housing, In: Commercial Chicken Production Manual 3^rd Ed. AVI Westport Connecticut.  
4. Barnwell, R. 1997. Evaporative cooling systems Cobb-Vantress Technical News Vol 5 No. 2.  
5. Swick, R. A. 1989. Effect of dietary acidulants and methionine sources on resistance of broilers to heat stress. Zootechnica, December 1989.  
6. Anon. 1988. Broiler Feeding and Management Guide. Arbor Acres. Glastonbury, Connecticut 
7. Anon. 1997. Hot weather management of broiler breeders. Ross Technical Service. Zootechnica International, April 1997.

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MITA (P) NO. 219/10/98 (Vol. PO40-1998)