Heat stress management in poultry by changing feeding strategy
Poultry meat and eggs are among the highest-quality human foods; these serve as important sources of animal protein in poor peoples to overcome the protein deficiency. Poultry is one of the best available sources for the production of high biological value animal protein. While hen egg production has tripled during the past 30 years. The worldwide rate of increase in the egg production has averaged 5.3% per year; while for chicken meat it was slightly higher at 5.7% per year. However, most countries in the hot regions of the world have daily per capita animal protein consumption below that recommended by the Food and Agriculture Organization(FAO) and the World Health Organization (WHO).
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| FEEDING STRATEGY TO COMBAT HEAT STRESS IN POULTRY |
Heat stress reduces the production performance of chicken leads to immunosuppression and increases the mortality rate in chicken. All the nutritional supplements (e.g. vitamins, zinc, Kcl) have functions in relation to heat stress. Suitable mineral and vitamin premixes can be developed for heat stressed chickens for improved performance, welfare and reducing feed cost. Heat stress increase the serum concentration of ACTH which increase corticosteroid level and in turns reduces the production. Poultry meat production has shown much higher growth than any other type of meat production.
The hot regions of the world have probably the greatest potential for further growth since the level of poultry meat consumption is still very low. There are several constraints to the future development of the poultry meat industry in the hot regions of the world. The availability of adequate supplies of grain and protein supplements necessary for the production of feeds is another major constraint for development. The most obvious constraint to high production regions is climate. High temperature, especially when coupled with high humidity, imposes severe stress on birds and leads to reduced performance. Certain nutritional manipulations and feeding practices that have been found to be helpful in reducing heat stress in broilers.
Poultry are homeotherm animals, which means that they are able to
maintain a constant body temperature by regulating metabolic heat
production and heat loss. In the ‘thermoneutral zone’ (20-24ºC) birds
are able to control their heat loss: body temperature is held constant,
feed intake is maximized and FCR is optimum. But as temperatures
increase, birds are not able to control their body temperature and it
starts rising above 41ºC.
Fully feathered broilers (about five weeks of age), layers and breeders
are the most sensitive to heat stress. Males are the most susceptible
because they produce more endogenous heat.
Heat Stress Index (HSI) is the sum of environmental temperature (when it
is above 27ºC) and relative humidity. This index is useful to determine
the onset of heat stress, that starts when the index is higher than
105.
Affected birds show signs such as:———
• Fast panting (from normal breathing of 25 breaths/minute to 250 breaths/minute). Panting causes respiratory alkalosis as blood carbon dioxide levels diminish due to hyperventilation. Respiratory alkalosis leads to an excess of bicarbonate in blood, which is eliminated through urine, eliminating also other important ions such as Na+, Ca2+, Mg2+, K+ and water.
• Birds lift their wings away from their bodies.
• Loss of appetite: At an environmental temperature of 28ºC, feed intake
is depressed by 12%. For every degree above 32ºC, the bird further
reduces its feed intake by 5%.
• Increase in water intake: bird increases its water intake by 4% for every 0.5ºC above 21ºC.
Metabolic (serious acid-base balance disorders, ascites), digestive (wet
droppings), skeletal (bone problems due to metabolic imbalance) and
respiratory disorders.
• Rise in cannibalism.
• Raise of mortality.
• Lethargy.
• Drop in productivity: In broilers, FCR worsens by 10-12% and growth
slows down by 5-10%. In layers and breeders, laying rate declines,
eggshell quality worsens, replacement pullets are lighter, lay later and
lay fewer eggs. In breeders, fertility is reduced, due to less mating,
poorer semen quality and female infertility.
IDEAL TEMPERATURE RANGE FOR DIFFERENT CLASSES OF POULTRY————-
Nutrition under temperature stress is one area of research that has
been receiving a great deal of attention for many years. But before
getting into specific nutrient requirements, it should be stated that
there is a great deal of disagreement to what is the ideal temperature
range for the different classes and age-groups of poultry. This is
possibly due to the fact that many factors influence the response of
poultry to temperature changes. Humidity of the atmosphere, wind
velocity and previous acclimatization of the bird are among the most
important. Birds, in general, perform well within a relatively
wide temperature range. The ideal temperature for broilers is 10-220C for
optimum body weight, and 15-270C for feed efficiency. While, layers
perform constantly well between a temperature range of 10-300C. Above
300C,production declines in terms of growth and egg production.
“Heat stress in poultry is a condition that occurs when birds have
difficulty in achieving a balance between its body heat production and
heat loss”.
The lack of sweat glands and relatively high body temperature make poultry, especially meat-type, fast-growing chickens, more susceptible to heat stress. During exposure to high ambient temperature, poultry face difficulties in maintaining body temperature. Their primary means of heat loss above upper critical temperature is by an increase in breathing rate (panting) and by raising their wings (to increase the surface area).
Heat is produced during the metabolic processes within the body, which
includes maintenance, growth and egg production. Heat production is
affected by bodyweight, species and breed, level of production, level of
feed intake, feed quality and, to a lesser extent, by the amount of
activity and exercise.
As the temperature rises, the birds undergo many changes such as
increased water consumption, respiration rate, body temperature,
inferior egg quality and susceptibility to diseases. Under stress
conditions, avian blood chemistry undergoes a change from acidic to
alkaline. There is a drop in the plasma, decreased level of vitamin C
in the adrenal cortex, a reduction in lymphocytes and a depression of
immune response. It is stated that levels of serum corticosteroids
increase as the result of the increased activity of the adrenal gland
due to stress, which then causes suppression of cell proliferation
factor or interleukin-2. All these conditions cause heavy economic
losses to the farmers.
Apart from temperature of the air ventilating the house, heat is also
added from the roof and walls. Much of the heat from working litter is
used to evaporate moisture and dry the litter. However, in hot weather,
damp litter will make heat stressed birds feel much more uncomfortable
than dry litter. In dry litter, birds will attempt to dust bath more
readily to aid cooling. The heat of electric lights and motors is a very
small fraction of that produced by the body metabolism (normally less
than 1%). Body heat is the dominant source of heat.
NUTRITIONAL APPROACHES TO ALLEVIATE HEAT STRESS————–
Negative effects of heat stress on the birds can be alleviated by different methods e.g.by increasing the ventilation rate, lowering the temperature where the birds are reared. But, due to high energy cost and structural issues these are not possible. So, alternative strategies must be known for the optimum performance of birds. One such tactic is nutritional manipulation. It usually involves ameliorating the diet to meet the altered needs of stressed birds.
Fasting——————–
Fasting reduces the heat production from digestion, absorption and metabolism of nutrients. Fasting also has a calming effect. Heat is generated in movement, through muscle contraction. This heat increase the body temperature hence chances of heat stress increases. Therefore, to reduce the heat load, broilers should be kept as calm as possible. This is especially important during the hottest part of the day.
Metabolizable Energy——————
Energy requirement decreases as the temperature increases above 21°C. This reduced requirement is mainly due to a reduction in energy requirements for maintenance, and the requirement for production is not influenced by environmental temperature. In contrast to winter energy consumption drops significantly during the summer or spring. Energy intake during the summer is 10–15% lower than during the winter. The use of high-energy rations for broilers has become quite common in warm regions. This practice should be accompanied by raising the levels of the most critical amino acids such as lysine and methionine. It has been found that significant weight response to additional energy only in the presence of relatively high levels of lysine. A diet energy response in warm weather is seen only when adequate amino acid levels are provided. This approach may increase performance, but it will also increase the heat load on the bird and its ability to survive.
Fat———————-
In the hot regions fat is commonly added in the poultry feed to boost the energy level of the feed. Addition of the fat in the feed reduces the specific dynamic effect of the feed and increase the energy intake which lessens due to high environmental temperature. There are several well-known effects of fat addition at high temperature. As the fat has lower heat of increment than carbohydrates and proteins so it reduces the heat production. Energy intake is increased in both broiler and laying hens in a warm environment by the addition of fat. The addition of fat to the diet appears to increase the energy value of the other feed constituents. Scientific studies revealed that a ration fed to broilers having 33% of the ME was supplied by fat consumed 10% more ME and 10% more protein and gained 9% more weight than chicks fed a low-fat ration.
Protein———————–
During heat stress birds mostly reduces the feed consumption which may result in reduction of essential nutrients like amino acids, proteins, minerals and vitamins. When their amount reaches critical level, this may result in reduction of egg size, shell thickness and egg production in case of laying birds. So, if the energy contents of the diet are increased, then there must be a proportional increase in all other nutrients. One of the strategy is to increase the protein contents of feed (from 16 to 18%) to meet the requirements of amino acids like isoleucine and tryptophan. However, increase indietary protein may cause increase in metabolic heat production. It has been reported that diets containing lower protein levels and supplemented with the limiting amino acids (methionine and lysine), give better results in summer as compared to high-protein diets. So, it better to improve the amino acid profile of feed by supplementation of limiting amino acids than increasing protein intake.
Vitamins———————–
Among various measures intended to reduce heat stress in birds, use of vitamins C, E and A in feeds is commonly practiced. Although poultry can synthesize vitamin C, but its synthesis is insufficient under stressful conditions such as low or high environmental temperature, high humidity, high egg production rate and parasite infestation. Such conditions, particularly in poultry, lead to generation of cytotoxic free radicals damaging the cells and cell membranes, increased protein catabolism, decreased protein biosynthesis and depletion of vitamin C. Vitamin C and E supplementations are reported to be beneficial in alleviating some of the heat stress related physiological responses and improving thermotolerance through their antioxidant effects. Dietary supplementation of vitamin C and E, particularly as a combination, improves productive performance, egg quality and antioxidant status of laying hens and other species of poultry. Vitamin C and E also exert a positive impact on egg shell quality of broiler breeder reared under heat stress conditions. Egg production also drops during hot weather. It might be related to the fact that during heat stress, hepatic synthesis of vitellogenine, a protein precursor for yolk formation, and its release into blood is impaired leading to decreased plasma vitellogenine concentrations and plasma/liver protein ratio. Dietary supplementation of vitamin E improves egg production by facilitating the release of vitellogenine from the liver and by increasing its concentration into blood. Various studies revealed that Vitamins A(15,000 mg/kg) + E (250 mg/kg) reduces heat stress related losses in broilers. While both vitamins E (65 mg/kg) and C(1000 mg/kg) enhance in vitro lymphocyte proliferative responses of heat stressed hens. Another study showed that high dietary supplementation of vitamin E (250mg/kg) is beneficial to egg production at higher temperatures. In addition, a recent study with broilers under heat stress conditions revealed that increased levels of vitamin E (100-200 IU/kg) improves the growth performance of birds,as well as the digestibility of crude protein, ether extract and gross energy.
Relationship of Vitamin A, E and C—————————-
Vitamin E is known to be a lipid component of biological membranes and is known to be amajor
chain-breaking antioxidant. Vitamin E is mainly found in the hydrocarbon
part of membrane lipid bilayer towards the membrane interface and in
close proximity to oxidase enzymes which initiate the production of free
radicals. Therefore vitamin E protects cells and tissues from oxidative
damage induced by free radicals.Vitamin A is involved in several
functions of the body including vision, differentiation of epithelial
cells, growth, and reproduction. The relationship between vitamin A and
vitamin E has been presumed in such a way that vitamin E appears to have
an important effect on the utilization and perhaps absorption of vitamin
A, and vitamin E protects, vitamin A from oxidative breakdown.
WhileVitamin C has been demonstrated to enhance antioxidant activity of
vitamin E by reducing the tocopheroxyl radicals back to their active form
of vitamin E or by sparing available vitamin E so, they exhibit synergic
properties. So, the supplementation of vitamins is helpful in reducing
the economic losses due to heat stress.
Acid–Base Balance and Electrolytes———————-
One of the consequences of heat stress is the change in the acid-base balance with the occurrence of respiratory alkalosis. Increased respiration rate (panting) leads to respiratory alkalosis. Excessive loss of carbon dioxide (CO2)during panting results in reduced partial pressure of CO2 in blood plasma. In turn, the level of bicarbonates rises in blood that causes a reduction in hydrogen ion concentration and thusan increase in plasma pH occurs. That is why most of the above mentioned practices failed, as these approaches did not take into account the disturbed acid-base balance(respiratory alkalosis) of birds during heat stress. Therefore, one of the best methods used to control heat stress is the monitoring of acid-base balance by supplementing feed or water with different electrolyte salts such as sodium bicarbonate (NaHCO3), potassium chloride (KCl), calcium chloride(CaC12) and ammonium chloride (NH4C1). These electrolytes, in different amounts and proportions, have been proved to be beneficial for poultry birds under heat stress. It is summarized from various studies that birds under heat stress perform best at a DEB of 250 mEq/kg and maintain their blood physiological parameters and blood nutrients well. Likewise in another study on heat-stressed broilers kept at a daily average of 23–31°C, reported that the optimum DEB is 190 mEq/kg for the starter period and 220 mEq/kg for grower and finisher.
Betaine (Natural):
Act as an osmolyte can help the birds to keep the water and ions balance during stress conditions and eventually improved performance in stress conditions. Maintaining the balance of water and ions within the cells is essential for the health of cells and, therefore, the health of the birds during the stress conditions. Betaine as a proven osmolyte, and has been shown to reduce the negative effects of heat stress on bird performance. It also increases gut tensile strength and reduces maintenance requirement by improving muscle hydration during stress conditions. When betaine accumulates in the muscle cell, cell hydration is improved. Hydrated muscle cells will synthesize more protein (e.g. as muscle) compared to dehydrated cells. Natural betaine as a methyl donor can provide the animals more efficiently with the methyl group and may reduce the feed cost by replacing some added methionine and choline chloride on the equivalent basis. Also after donating its 3 methyl groups, betaine (trimethylglycine) becomes glycine. The amino acid glycine is involved in the synthesis of the amino acid serine; both glycine and serine are building blocks for protein e.g. breast muscle.
Minerals—————————-
Egg weight and eggshell strength decline at high environmental temperatures. This appears to be partly due to reduced calcium intake, but several physiological mechanisms are involved,reduced blood flow through shell gland due to peripheral vasodilatation, respiratory alkalosis, reduced blood ionic calcium content, reduced carbonic anhydrase in shell gland and kidneys and reduced Ca mobilization from bone stores. Different minerals like NaHCO3, KCl, CaCl2 and NH4Clalso help in reducing heat stress by balancing acid-base and ionic balance.
WAYS OF HANDLING HEAT STRESS DURING SUMMER—–
1. Plant shade trees around the poultry house.
2. Reduce the thickness of the old built-up litter. Two inches of fresh litter may be provided in the place of old litter.
3. Hang wet gunny bags on the sides.
4. Stocking density If the higher the bird density in farm, more heat
will be produced. Birds in density stocked barns tend to absorb each
other’s radiant heat load, which makes more difficult heat management
for broilers. Reducing the bird density in summer will give more floor
space per bird and allow more heat to escape from underneath their
bodies and from the litter.
5. Evaporative cooling Sprinklers are commonly used for evaporative
cooling when temperatures are more then 79- 86°F (26-30°C). Too much
water can actually increases the barn to dangerous level. Generally
foggers reduce the temperature of shed up to 5-10°C.
6. Ventilation Proper ventilation is crucial for heat stress management.
A good ventilation system performs the following——
• Remove moisture laden air from the broiler house. • Brings in an equal amount of fresh outside air. • Directs incoming air to all areas equally. • Keeps inside air moving to flush hot, humid air from between the birds. • Providing exhaust fans on one side and pad cooling on other side with complete sealing of sheds side will bring down the temperature of below 8°C.
7. Flock walking helps to alleviate heat stress The purpose of flock walking is to make birds release heat trapped under body. If this is carried out before birds shows the signs of stress. If the birds are very quite (or) have heads drooping, it is probably best not to disturb them any further. 8. Nutritional strategies to reduce heat stress in broilers The most important factor affecting performance in broilers subjected to high temperature is reduced feed intake. Feed conversion in broilers is subject to marked fluctuations because of seasonal as well as ambient temperature changes. High temperatures reduce the efficiency of utilizing feed energy for productive purposes. Broilers not only eat less at high temperature, but also gain less per unit of intake, especially at temperatures above 30°C.
Conclusion
A range of intervention strategies to alleviate heat stress conditions in broilers and layers including environmental management (such as facilities design, ventilation, sprinkling, shading, etc.), nutritional manipulation (i.e., diet formulation according to the metabolic condition of the birds), as well as inclusion of feed additives in the diet (e.g., antioxidants, vitamins, minerals, probiotics, prebiotics, essential oils, etc.) and water supplementation with electrolytes.