May 11, 2011
I wish to add some following points thoroughly to overcome the problem of heat stress :
Heat Stress & 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
Methods of Heat Loss
During the summer months, when daily temperatures regularly reach the mid- to upper 90s, 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 105oF. 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 (55o 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.
Sensible Heat Loss Methods
Flow of thermal energy without the aid of a material medium between two surfaces All surfaces radiate heat and receive radiation back; the net radiation heat flow is from higher to lower temperature surfaces.
Thermal energy flow through a medium or between objects in physical contact. Direction of energy transfer depends on a temperature gradient; heat moves from areas of higher to lower temperature.
Heat flow through a fluid medium such as air; thermal energy moves by conduction between a solid surface and the layer of air next to the surface, and the thermal energy is carried away by the flow of air over the surface. Energy transfer to the air depends on temperature and movement of air across the skin surface; heat is transferred to air moving across the skin surface if the air is at a lower temperature than the skin.
Latent Heat Loss Method
The transfer of heat when a liquid is converted to a gas; when water is converted from a liquid to a vapor, heat is utilized. Energy transfer is influenced by the relative humidity, temperature, and air movement; heat is transferred from the animal's body to water, turning it to water vapor.
Once the environmental temperature reaches approximately 77°F, the method of heat loss begins shifting from sensible to evaporative heat loss. 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.
Physiological Effects of Panting
Panting removes heat by the evaporation of water from the moist lining of the respiratory tract. However, panting itself generates body heat, and it causes poultry to eliminate water from the body. It can induce respiratory alkalosis, which occurs because the bird "blows off" excessive carbon dioxide (CO2) when it pants. As a result, body fluids become more alkaline, causing the kidneys to excrete excessive amounts of several electrolytes. As the shift in body fluid pH occurs, feed intake is increasingly depressed, adversely affecting growth, production, and overall performance of the bird. During the hot summer months, evaporative heat loss typically becomes the primary method by which birds regulate their body temperature unless proper ventilation is provided and other steps are taken to reduce heat stress.
Feed and Feeder Management
Any management technique that increases nutrient intake during heat stress will minimize the drop in production efficiency. Three easy ways to increase nutrient consumption are to increase nutrient density, take advantage of natural increases in feed consumption at certain times of the day, and adjust ventilation fans to provide more cooling during the evening. A very direct way to ensure optimum nutrient intake despite decreases in feed consumption is to increase the nutrient density of the ration. Recent research indicates that low phosphorus consumption can contribute to increased heat prostration losses. A second alternative is to feed the birds at the time of day when feed consumption is highest. The light-to-dark cycle results in a U-shaped feed consumption curve. Shortly after light come on, feed consumption is high. It gradually declines during midday and then increases about 1 hour before lights are turned off. If birds are fed during the cool part of the day, feed consumption will be higher. Birds should not be fed during the afternoon in periods of hot weather since this will increase the amount of body heat that they must dissipate and thus increase the potential for heat prostration. Abrupt changes in feeding times should be avoided. A third technique is to cool the birds as much as possible during the evening hours. Hens or meat birds tend to build up body heat during extended periods of hot weather. If their body temperature can be reduced during the evening , the birds will be able to consume more feed in the early morning. The house can bee cooled in the evening by setting the fan thermostats so that the fans will continue to run until the internal house temperature reaches 75°F (65°F for mature birds).
Under hot and humid conditions, feed should not be stored for longer than a week.
The bird's body temperature increases after feed ingestion due to the thermogenic processes of digestion and metabolism. With morning feeding, the thermogenic effect coincides with the rising environmental
temperature, aggravating heat stress, The thermogenic effect lasts for 8-10 hours at 35°C, compared to just 2 hours at /20°C./ Metabolic heat production is 20-70% less in starved birds than in fed birds. Therefore,
during hot weather, birds should be deprived of feed while the temperature is reaching and at its peak. Feeding during early and late hours of the day will help to minimize growth checks and mortality in broilers. Intermittent feeding, i.e. providing the light for 30 minutes followed by 3 hours dark, may also reduce the activity (heat production) of the bird but 20-30% more feeder and waterier space will be required.
For layers, feeding during later part of the day will ensure sufficient calcium is available for optimum shell calcification, Low feed intake is the main cause of poor performance at high temperatures. The following practices can help to raise feed consumption and may be worthwhile considering:
Wet mash feeding
pellet or crumble form of feed
Low-calcium diets with choice feeding of calcium sources
Frequent feeding and stirring of feed in the feeder
Addition of fat or molasses so to increase feed palatability.
Layers will produce eggs constantly in the temperature range of 10-30°C. Above 30°C, performance will be depressed in terms of growth, feed intake, egg production, egg size and eggshell quality. Nutritional imbalances can also result from poor quality control and lack of regulations for feeds, feed ingredients and feed additives.
Furthermore, mycotoxins develop very quickly in hot and humid conditions, leading to loss of production, immunosuppression and higher mortality. Routine management practices, e.g. medication, vaccination,
beak trimming etc, also add to the stress.
Energy intake is the most important nutrient limiting bird performance at high temperatures. The energy requirement for maintenance decreases by about 30kcal/day with increase in environmental temperature above 21
°C. Although the energy requirement for maintenance is lower at higher temperatures, most of the energy is wasted in heat dissipation so the absolute energy requirement is not affected by heat stress. The feed energy concentration should be adjusted to allow for the reduction in feed intake at higher temperatures. Feed intake changes
about 1.72% for every 1°C variation in ambient temperature between 18 and 32°C. However, the decline is much faster (5% for each 1°C) when the temperature rises to 32-38°C. Measures to increase feed intake include
the inclusion of fat in the diet. Feed consumption increased up to 17% by 5% fat supplementation in heat stressed birds because fat improves palatability. In addition, fat offers an extra calorific value by decreasing the rate of passage of digest a, thereby increasing the utilization of nutrients.
Fats or oils with more saturated fatty acids are preferred in hot humid climates. The concentration of energy should be increased by 10% during heat stress, whilst the concentration of other nutrients should be increased by 25%.
The requirements for protein and amino acids are independent of environmental temperature so heat stress does not affect bird performance as long as the protein requirement is met. However, heat stress reduces feed intake and the levels of protein/amino acids need to be increased with the environmental temperature up to 30°C. At even higher temperatures, heat stress has a direct effect on production and there is no benefit in raising the protein level.
The correct amino acid balance in the diet minimizes fat deposition in the liver, thereby increasing the survival of birds under heat stress. So, a low protein diet with balanced critical amino acids (methionine and lysine) is more beneficial than a diet high in total protein during hot periods. The oxidation of excess protein or amino acids generates metabolic heat.
CALCIMU AND PHOSPHORUS:
Heat stress reduces calcium intake and the conversion of vitamin D3 to its metabolically active form, ,25(OH)2D3, which is essential for the absorption and utilization of calcium. In effect, the calcium
requirement of layers, particularly older birds, is increased at high environmental temperatures. To overcome this effect, extra calcium should be provided at the rate of I g/bird in the summer months in the form of oyster shell grit or limestone. Supplementation should be made over the normal dietary calcium level (3.75g/bird/d) recommended for layers.
However, excessive levels of calcium reduce feed intake due to the physiological limit of calcium appetite and also reduced palatability Instead of increasing the diet specification, the calcium should be offered separately as a choice feed. Better results are obtained by offering the calcium source in the afternoon. The optimum particle size is the one that supplies the required calcium at me time of shell formation. The minimum size to improve gizzard retention is about 1mm.The phosphorus level in diet must not be forgotten as excessive
phosphorus inhibits the release of bone calcium and the formation of calcium carbonate in shell gland, thereby reducing the shell quality.
ELECTROLYTES AND BUFFERING AGENTS
Supplementing the diet with 0.5% sodium bicarbonate or 0.3-1.0% ammonium chloride or sodium zeolites can alleviate the alkalosis caused by heat stress. Sodium bicarbonate stimulates feed and .water intake at high
environmental temperature. The body weight gain can be increased up to 9% by addition of these chemicals in the feed of heat-stressed broilers.
The excretion of potassium through urine is significantly higher at 35°C than at 24°C. The potassium requirement increases from 0.4-0.6% with a rise in temperature from 25 to 38°C. A daily potassium intake of
1.8-2.3g potassium is needed by each bird for maximum weight gain under hot conditions.
To compensate for the reduced feed intake under heat stress, dietary allowances for electrolytes (sodium, potassium and chloride) may be increased by 1.5% for each 1°C rise in temperature above 20°C.
Electrolytes are also present in the drinking water and these levels need to be taken into consideration. Excess intake of electrolytes can lead to wet droppings, Potassium chloride can be added to the drinking water (to give 0.24-0.30% K) but care must be taken to avoid imbalances. Excess chloride is known to decrease the blood bicarbonate concentration.
During heat stress, the bird tries to maintain its body temperature by increased respiration, i.e. evaporation of metabolic water, which may considerably increase the water requirement. The addition of electrolytes (and/or vitamin C) to cold water helps to increasing feed intake by heat stressed birds.
Additional allowances of ascorbic acid (vitamin C), vitamins A, E, and D3 and thiamine can improve bird performance at higher temperatures. However, the loss of vitamin activity either in premix or in feed during storage particularly at elevated environmental temperature is a prime concern and probably explains the conflicting results on the effects of vitamin supplementation during heat stress. High temperature, moisture, rancid fats, trace minerals and choline speed up the denaturation of vitamins. Vitamin activity in feeds can be maintained by using feed antioxidants, gelatin encapsulated vitamins, appropriate storing conditions and adding choline and trace minerals separately from other
Ascorbic acid synthesis is decreased at elevated environmental temperature, making it an essential dietary supplement during the summer. The vitamin helps to control the increase in body temperature and plasma corticosterone concentration. It also improves eggshell quality via its role in the formation of the shell's organic matrix. Furthermore, it protects the immune system and reduces mortality in growing birds infected with IBD in a hot environment by protecting the lymphoid organs and thyroid activity. Supplementation of ascorbic acid (200-600mg/kg diet) improves growth, egg production, number of hatching eggs, feed efficiency, egg weight, shell quality and livability during heat stress.
The absorption of vitamin A declines at high temperatures. In broiler breeders, a three fold increase in supplementation has been found to be beneficial.
Vitamin E protects the cell membrane and boosts the immune system so additional dietary supplementation may be advantageous during hot weather. Mortality due to E. coli infection reduced significantly by supplementation of vitamin E in diet.
Heat stress is known to interfere with the conversion of vitamin D3 to its metabolically active form, i.e. 1,25(OH)2D3, so higher dietary levels maybe justified during periods of high temperature. The active form of vitamin D3 is involved in the synthesis of calcium binding protein, essential for calcium and phosphorus homeostasis.
A number of compounds are effective in reducing the ill effects associated with hyperthermia although their cost may be prohibitive.Antipyretic compounds, e.g. salicylic acid and aspirin, minimize the levels of catecholamine in the blood during heat stress.
The performance of heat stressed birds can be increased with magnesium aspartate, zinc Sulphate, diazepam, metyrapone or clonidine in the feed. Aureomycin has been found lo alleviate the stress (growth depression) caused by injection of foreign protein or salmonella end toxin but it has not always been found to be beneficial.
Acetylsalicylic acid (3% of the diet) increased me weight gain and shell quality in some reports but the
effects are inconsistent. Resin pine, an alkaloid from the Rawolfia plant is known to prevent the loss of carbon dioxide from birds subjected to high environmental temperature, thus stabilizing the blood acid base balance.
Flunixin, an anti inflammatory analgesic drug at 0.28-2.2mg/kg bodyweight per day increased water consumption by 150-300ml/bird/day. The anticoccidial compound, nicarbazine (at the standard dose of 125mg/kg), has increased the mortality of broilers to up to 90% during heat stress.
Adding potassium chloride in drinking water can ameliorate the toxic effects.
Techniques for Managing Heat Stress
A grass cover on the grounds surrounding the poultry house will reduce the reflection of sunlight into the house. Vegetation should be kept trimmed to avoid blocking air movement and to help reduce rodent problems. Shade trees should be located where they do not restrict air movement. Fans should be routinely maintained. Maintenance should include cleaning the fan and keeping pulleys and belts in good condition and properly adjusted. Poultry netting on sidewalls or air inlets often will pick up enough dust to restrict air movement and should be cleaned regularly. Keeping a reliable, clean, cool source of water available to poultry is essential to help the birds cope with high temperatures. Because the birds excrete electrolytes during periods of heat stress, electrolytes can be added to the drinking water to replace those that are lost and to stimulate water consumption. Avoid placing water pipes near the ceiling where the water will gain extra heat. Line in which the water has become warm can be drained to allow cooler water to reach the waterers. A second well or access to an emergency source of water should be available in case the primary water source fails. Another factor that affects heat gain of a house is the condition of the roof. A shiny surface can reflect twice as much solar radiation as a rusty or dark metal roof. Roofs should be kept free of dust and rust. Roof reflectivity can be increased by cleaning and painting the surface with a metallic zinc paint or by installing an aluminum roof. These practices are particularly effective for buildings that are under insulated.
Equipment and Ventilation Techniques for Reducing Heat Stress
During the summer when the temperature and humidity are high, proper poultry house ventilation is vital to ensure the necessary removal of heat and the continued productivity of the flock. Poultry house ventilation systems have a number of components. These include curtains, fans, fogging nozzles, evaporative cooling pads, timers, static pressure controllers, and thermostats. Most ventilation systems can provide an adequate indoor environment when properly managed. If the design and management of the ventilation system fails to satisfy the flock's ventilation needs, stale, contaminated air can build up in the poultry house. Stale air and contaminants, including ammonia, moisture carbon dioxide, carbon monoxide, and dust, can cause stress and lead to depressed performance. Stress may impair the immune system and increase susceptibility to disease. To reduce problems with stale air and contaminants, air temperature, air speed, and relative humidity must be controlled by careful management of the ventilation system.
Curtain-sided houses rely extensively on natural air movement. These houses work best when they are located away from obstructions such as other buildings or trees that can block natural air currents. To avoid total reliance on natural air movement, most producers have added circulation fans in curtain houses to increase air movement and promote the loss of body heat from the birds. These fans should be spaced and positioned to maintain air movement between fans and to direct their flow in a way that will increase the turbulent air movement around the birds. Spacing of the fans depends somewhat on their size, but they are generally spaced about 25 to 30 feet apart in curtain layer houses and 40 to 50 feet apart in broiler houses. Circulation fans should be controlled by thermostats set at about 85 o F (or lower in hot weather). To save energy, the fans should shut off when the temperature drops below 85 o F except during periods of extended hot weather. At those times, it is advantageous to leave the circulation fans running through the cool evening hours by turning the thermostats down to 75 o F or even lower. This practice will lower the inside temperature faster, providing the birds with a cooler environment in which to dissipate stored body heat.
Foggers reduce air temperature in the house on hot days (90 o to 95 o F) when humidity is low, especially during midday when humidity levels are lowest and temperature is highest. The foggers inject fine water particles into the warm inside air. As the water vaporizes, heat is absorbed from the air, lowering its effective temperature. When foggers are used, they should be operated intermittently or designed to avoid excessive water flow into the environment. If too much water flows through the foggers, humidity levels may increase to the point where birds can no longer cool themselves by evaporation. In addition, litter made wet by excessive fogging can lead to performance and health problems. The appropriate water flow rate and timer settings depend on the method of ventilation, ventilation rate, bird size, and outdoor conditions. Fogging systems in naturally ventilated house are typically designed for a water flow rate of 50 to 100 gallons per hour.
In forced ventilation systems, all air movement is produced by fans in the building walls. Houses that use this type of ventilation are also referred to as controlled environment systems. Power ventilation houses can provide good, uniform airflow patterns under hot summer conditions if correct static pressure is maintained and airflow obstructions are avoided. It is very important to determine how much air should be moved through the building. This can be accomplished in two ways. Approximate values for the minimum volume of air required per pound of poultry body weight are given in Table 3. These values can be used to determine the total fan capacity required for the house. Keep in mind, however, that the rates shown are minimum estimates, and it is best to plan for the worst possible case. For example, the efficiency of fans is greatly reduced if they are allowed to become excessively dirty, reducing the airflow through the building.