Effect of Heat Stress on Poultry Production and the  Managemental Approaches to Minimize Heat Stress in Broiler and Layer Chickens

Chickens are very vulnerable and at risk of overheating due to heat stress in hot and humid weather. Chickens have no sweat glands and have to pant to get rid of body heat by other means. Chickens often raise their wings to radiate heat from poorly feathered areas. This requires more energy from the chicken than just sweating. Eventually, without relief from the heat, chickens will often become exhausted from heat exhaustion and heat stress. When chickens pant excessively, it increases their respiratory rate, which in turn affects egg laying, growth rates or even lead to higher mortality.

What is Heat Stress? 

Chickens are very sensitive to high temperatures and their ability to lose body heat is limited by their plumage, high metabolic activity and the absence of sweat glands. Heat stress usually occurs when chickens are exposed to high ambient temperatures and in combination with low air velocity and high relative humidity.

It is the environmental temperature in combination with the humidity level that determines the level of heat stress. See the image below, which shows that a humidity level between 45 and 75 % in combination with a temperature below 30 °C is comfortable for chickens.

The intricacy to achieve a balance between body heat production and body heat loss leads to heat stress in broiler and layer chickens. Heat stress has severe and economical effects on chickens and occurs due to high relative humidity and low air speed. The unfavorable effects of heat stress comprises of high mortality, decreased feed consumption, poor body weight gain and meat quality in broiler chickens whereas poor laying rate, egg weight and shell quality in laying hens . In broilers and turkeys, it can also lead to poor feed conversion. Major factors which increase the susceptibility of birds for heat stress include genetics, feather cover, high stocking density, acclimation, drinking water temperature and availability. Heat production is affected by body weight, species and breed, level of production, level of feed intake, feed quality and to a lesser extent by the amount of activity and exercise. If the stocking density is too high for the size of house and ventilation equipment then due to addition of more metabolic heat addition to house air, temperature may rise perilously. Feather cover and size of comb and wattles are characteristics of the birds which affect heat loss. According to Deeb and Cahaner (2001) , enormity of the decrease in body weight and body weight gain at high temperature (30°C) appears to be associated with high growth rate at normal environment (25°C). Fast growing broilers produce more heat and effect of heat stress is more prominent in commercial broiler stocks and broilers with high growth potential compared to the slower-growing chickens  reported that during high temperature fast growing broilers have more mortality as compared to slower growing broilers. The rise in environmental temperature more than upper critical limit in birds cause opposite response and produce various effects like blood circulation to skin, comb, wattles and upper respiratory tract increases two to four times. Consequently blood flow to liver, intestine, kidneys is reduced and birds stretch the body and take lying position closer to litter material and nearer to water pots or cooler. Water consumption increases by 1.2 to 3.2 times as per outside temperature and birds start panting (increase in respiratory and heart rates).

TOLERANCE TO HOT WEATHER CONDITIONS

Broiler and layer chickens can tolerate to some extent steady change of season to summer but if temperature rises suddenly, it results in heavy mortality. It is also reported that chicks exposed to higher brooding temperature during first few days are able to tolerate heat stress better in later life. Relative humidity in air greatly influences tolerance to heat stress. High temperature and relative humidity form a lethal combination for broiler and layer chickens (Table 1) and these conditions exist in coastal regions of India.

Effect of temperature and relative humidity on broiler and layer chickens.

 Environmental temperature (̊C) -Environmental relative humidity (RH) –Consequence

20–26                                             Up to 40%                                               Optimum

26–30 40 –                                        75%                                                     Harsh

30–40                                         Up to 45%                                          Progressively extreme

30–40                                            65% and above                                                 Impossible

SIGNS AND SYMPTOMS OF HEAT STRESS

There is depressed appetite and more water consumption. Respiration rates increases even beyond 250 breaths/minutes in severe cases and panting and gasping is quite common. Birds look lethargic and keep their eyes closed, legs and wings outstretched. Birds try to lose heat by adjusting their feather position. Extremely pale comb and wattles and prostration are also common. There is drop in egg production, decreased egg size, egg weight and poor shell quality. During heat stress loss in body weight and increased cannibalism is also there. Laying hens are susceptible to heat exhaustion. Egg layers also require large amounts of calcium to avoid soft eggshells. When hot, hens may not eat as much so calcium consumption is low. Prolonged exposure to hot weather will lead to following harmful effects. a. Imbalance of Acid-Base Equilibrium in the Body of Birds: Loss of carbon dioxide (CO2) because of continuous panting which results in increased blood pH or alkalosis in birds. Kidneys maintain acid-base balance by renal exchange of bicarbonates with chloride ion. This results in increased excretion of bicarbonates in urine and retention of chloride in plasma and that leads to systemic acidosis. Thus in heat stress initial alkalosis changes to systemic acidosis and birds dies due to acid shock. Diets containing ammonium chloride (0.3– 1%) and sodium bicarbonate (1–2%) are useful in heat stress because ammonium chloride reduces blood pH and sodium bicarbonate prevents excessive acidosis. Electrolytes are also excreted in urine along with bicarbonates because bicarbonates are negatively charged and Na and K ions which are important electrolytes being positively charged are excreted with bicarbonates. Loss of electrolytes affects the water balance or acid-base Imbalance in the body of birds. b. Blood Supply to Visceral Organs Decreases leads to poor weight gain, higher FCR (due to impaired digestion and assimilation) and enteritis. c. Imbalance of Water in the Body of Birds: Normally water intake and water formed by oxidative metabolism in body is equal to the water loss through urine, faeces, respiration and evaporation. However, water loss is more through urine and respiration in heat stress and this leads to dehydration or decrease in extra cellular fluid level, fall in blood volume, blood pressure and rise in plasma osmolality. In this condition body releasing Renin from kidney cells and that increases thirst in the body. Vasopressin or anti diuretic hormone is released from pituitary gland which reduces urine output by increasing water resorption in renal tubules. There is less retention of water in cells is less because of loss of electrolytes and organic osmolytes (Betain, Sorbitol, Inositol), although birds drink more water. Negative water balance prevents internal cooling and hence there is further rise in body temperature. Water balance in the body cells against extra cellular osmotic gradients can be maintained through supplementation of osmolytes and electrolytes. d. Decrease Immunity or Immune Suppression: In hot weather there is release of corticosteroids from adrenals and also depletion of plasma Vitamin C and reduction in lymphocyte count. The effect is immune suppression.

POST-MORTEM LESIONS

These include congestion of carcass, mucoid exudate in nostrils and mouth. In dead birds autolytic changes set in fast and post mortem examination of fresh carcasses may have engorgement of subcutaneous capillaries, congestion of abdominal and breast muscles, congestion of trachea, combs and wattles. DIAGNOSIS Diagnosis of heat stress can be done on the basis of signs and symptoms such as temperature recording. Efflux of Creatinine kinase from cells to plasma is there due to increase in intracellular calcium concentration. Elevation of plasma creatinine kinase is indicator of heat stress in chickens. But it is not necessary to conduct routine laboratory tests to diagnose heat stress condition.

PREVENTIVE MEASURES TO MINIMIZE HEAT STRESS

Housing Management Houses of optimal height and insulation, painted white to reflect heat, evaporative coolers, plays a very important role in reducing heat stress. Well located and well laid out broiler and layer farms, with trees and lawns around and getting good breeze will have lesser problems in summer season. In addition, roof insulation plus increased ventilation by fans would help to withstand moderate hot weather. In extremely hot weather, these measures are not sufficient and evaporative cooling systems like sprinklers, foggers, or pad cooling are necessary. These systems work very well especially if relative humidity is low and temperature inside houses can be brought down by 10 to 15°C. Apply of fans without use of evaporative cooling system may be dangerous in intense hot weather conditions since it is only hot air that is blown in to the chicken house. In extremely hot weather condition, in deep litter system, if we can increase the quantity or number of earthen pot, it reduces heat stress to some extent.

Feeding Management

Feeding during cooler hours may be beneficial because digestion leads to production of heat. Feed withdrawal from 9 am to 4.30 pm is very effective in reducing heat stress mortality in birds. There is production of nearly 7% additional heat in the body due to feed intake and digestion which is maximum 4 to 5 hours after feed intake. This should not coincide with hottest part of the day (1 to 3 pm). Birds fasted in the day compensate intake in the night time.

Following feeding interventions should be adopted to manage heat stress in birds as follows:

• Increase the energy level of the diet (2850 kcal ME/kg minimum) ideally by incorporation of fats or oils. Limit the use of fibrous ingredients if possible. According to Zhou and Yamamoto (1997) , there is increase in heat production with feeding level.

• Reduce crude protein component (17% CP maximum) while maintaining daily intakes of methionine (360 mg) and lysine (720 mg). According to Temin et al. (2000) , decreased protein synthesis cannot be restored by high dietary protein level in broiler and layer chickens. High dietary protein levels at high temperature reduce both growth rates as well as meat yield in fast growing commercial broiler chickens .

• Fat should be increased by 2 to 3% at the cost of carbohydrates without changing metabolisable energy (ME). Fats are good in summer because their heat increment value is lowest, give better cooling effect in body because of higher water content and fat stimulates feed consumption.

• Mineral-vitamin premix is important component in feed of layer and broiler feed. Maintain daily intakes of calcium (3.5 g) and available phosphorus (400 mg). In an experiment conducted by Kucuk et al. (2003) , zinc supplementation resulted in an improved live weight gain, feed efficiency and carcass traits.

• Vitamin C: There is increased demand for vitamin C by adrenal glands for controlled production of hormones required for gluconeogenesis because of release of corticosteroids in heat stress. In heat stress there is also reduced synthesis and partial depletion of vitamin C. Inclusion of vitamin C at 200-400 g/ton of feed is recommended in summer months. If incorporated in feed of chicken then no need to give in water again. Vitamin C supplementation increase carcass quality and carcass CP content as well as reducing carcass crude fat content in chicken . Ferket and Qureshi (1992) reported vitamin supplementation to be beneficial for the performance and immune function of heat-stressed chickens.

• Antioxidants: In heat stress there is excessive oxidative metabolism and release of free radicals in the body. Free radicals damage all types of biological molecules and cells of vital organs. Vitamin E captures and neutralizes free radicals and its inclusion at 50 to 100 ppm in feed is advisable. Vitamin C also has antioxidant property.

• Toxin binders: In wet summer, there is rapid growth and toxin formation in feed. Good quality toxin binders at higher dose should be used in feed.

Cold Water

Cool water should be supplied continuously to birds. Watering space should be doubled. Overhead tanks and pipe system should be properly covered to keep the water cool. Providing fresh cool water (5°C) in noon time is very effective for internal cooling of body and reducing symptoms of stress. Branton et al. (1986)  and Balnave and Oliva (1991)  reported that supplementation of electrolytes in water increases water consumption and in turn tolerance to heat stress. Increased water consumption in chickens has no negative effect on the meat quality .

Stocking Density

Adequate ventilation should be provided as per number of birds housed. Stocking densities should not be exceeded more than recommended numbers and during hot weather stocking density should be less in shed as well as during transport to avoid overcrowding. The house structure should be sufficiently insulated to avoid solar heat radiations. There should be proper maintenance and regular testing of emergency ventilation equipments. Summer heat places enough stress on birds so unnecessary activities should be avoided during the hottest time of the day to minimize stress.

Vaccination Time

Strict cold chain should be maintained during transport storage and administration of vaccines. Vaccination should be carried out during cool hours. Immunostimulants like avetotal (combination of levamisole, fructose, electrolytes and vitamins) should be given for three days following each vaccination.

Heat stress response to maintain normal body temperature-

• Increased panting
• Spreading of wings
• Moving toward shades or towards the place where airflow is more
• Blood-swollen wattles and comb
• Diverting blood from internal organ to the skin which darkens skin colour
• Reduced physical activity
• Lesser feed intake and drinks more water which can cause loose droppings

Impact on poultry production

Heat stress production losses depend on multiple factors like maximum temperature, duration of high temperatures, rate of temperature change, and relative humidity of the air leading to the following impacts –

⬆ Mortality                  ⬇ Feed intake

⬇ Gut health              ⬆ CFCR

⬇ Body weight           ⬇ Meat quality

⬇ Immunity                ⬇ Egg production

⬇ Egg weight              ⬇ Egg shell quality

⬇ Albumin height       ⬇ Hatchability

Impact of heat stress on Egg shell quality

Panting due to heat stress can cause an acid-base imbalance in the blood of layers, resulting in thinner and weaker eggshell. Hyperventilation in birds to regulate body temperature leads to excessive loss of CO₂ gas from the lungs and blood, resulting in an increase in blood pH or a shift towards alkalinity, a condition referred to as respiratory alkalosis. A rise in blood pH levels reduces the activity of carbonic anhydrase enzyme, causing a decrease in the transfer of calcium and carbonate ions from the blood to the shell gland. The addition of calcium to the diet alone cannot rectify this issue. A reduction in feed intake and an increase in phosphorus loss leads to a decrease in calcium consumption, which is another factor contributing to thin eggshells. To restore acid-base balance, use of potassium chloride, ammonium chloride, or sodium bicarbonate is recommended.

General guide to the reaction of adult poultry to various temperatures

55 to 75 ⁰F	Thermal neutral zone. the temperature range where a bird can maintain its body temperature without any need to modify its basic metabolic rate or behavior.
65 to 75 ⁰F	Ideal temperature range.
75 to 85 ⁰F	A slight reduction in feed consumption can be expected, but if nutrient intake is adequate, production efficiency is good. Egg size could potentially decrease, and the quality of the eggshell may deteriorate when temperatures approach the upper limit of this range.
85 to 90 ⁰F	Feed consumption falls further. Weight gains are lower. Egg size and shell quality tend to decline. Egg production usually suffers. It is recommended to implement cooling measures prior to reaching this temperature range.
90 to 95 ⁰F	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 ⁰F	Heat prostration is probable. Emergency measures may be needed. Egg production and feed consumption are severely reduced. Water consumption is very high
Over 100 ⁰F	At these temperatures, the priority is the survival of birds, and as such, urgent measures must be taken to cool them

 

Fig.1 – Diagram of Thermoneutral Zone

Strategies to reduce heat stress in poultry

Heat stress reduction in poultry can be achieved by implementing various strategies. Two key strategies are housing management and nutritional management. Housing management involves adjusting the environment in which the birds are kept, including ventilation, temperature control, and lighting. Nutritional management involves providing birds with a balanced diet that includes specific nutrients that can help them cope with heat stress. Both strategies can be effective in reducing heat stress and maintaining performance. Monitoring the temperature and humidity at farm is a critical task during implementation of heat stress mitigation strategies.

1. Housing management

• Need to manage routine work and management practice schedule so that birds won’t disturb in hotter period of day
• Reduce the intensity of light in hot period to decrease physical activity of birds.
• Reschedule lightning program to make more morning light hours and less afternoon light hours to increase feed intake.
• Growing trees on both side of shed as well as covering of roof with Agri waste, dry coconut leaves or whitewash helps to reduce temperature.
• Installation of water tank inside the shed is preferable but if water tank outside the shed, then pandhal and whitewash for water tank required.
• Wet gunny on the side mesh to cool down the surrounding environment.
• Sprinkler on the roof and Foggers inside the shed, whereas usage should be limited in case of high humidity in the air.
• Fans & foggers start before 1 hour of heat increment and stop 30 minutes after panting stops. Run the foggers for 2 minutes every 20 minutes.
• Clean drinkers & flush out water from pipeline frequently in nipple system. Additionally, maintaining the appropriate height, pressure, and water flow (> 70 ml/minute/nipple drinker) of the nipples is also crucial.
• Water pipeline should be covered with gunny bag or Agri waste, underground pipeline is desirable during farmhouse construction.
• Increasing space to avoid overcrowding of birds or Removing 20 to 30 % birds after 30 days in broiler to avoid heat stress mortality in birds having higher body weight.

2. Nutritional Management

• Feed distribution at early morning & evening time (Cool part of the day) to increase the feed intake. Normally 1/3 part of feed in early morning and 2/3 part in evening to maintain eggshell quality.
• Feed intake can be increased by wet mash feeding and crumble or pellet type feed with the addition of fat or molasses to increase palatability.
• Mash feed is preferred in broiler during extreme heat stress if feed is offered ad-libitum and removal of feed is not possible to prevent mortality in higher age of production cycle (age >30 days)
• Withdrawal of feed (9 am to 4:30 pm) before anticipated time of peak temperature.
• Feed should be made denser with nutrients, vitamins, and minerals to compensate for reduced feed intake.
• Usage of vegetable or highly digestible protein sources in feed is recommended.
• Formulate to digestible amino acid targets and do not apply a high crude protein minimum in the formula. Incorporation of Synthetic amino acids can reduce crude protein in the diet without limiting amino acid levels.
• Usage of Fats or oils with more saturated fatty acids are crucial to adjust feed energy concentration rather than carbohydrate or proteins, to compensate the reduced energy intake due to less feed intake during the hotter periods.
• Oils content Linoleic acid which enhances performance and egg weights as well as oil increases palatability of feed and generates less body heat as compared to carbohydrates and protein sources.
• C and Vit. E are useful in diet because of their anti-heat stress/antioxidant properties. Inclusion Level of these vitamins in the feed can be increased in summer to improve immunity.
• Betaine helps in water retention, increased anabolic activity, maintained integrity of cells during heat stress condition. Additionally, betaine enhances production performance by supplying methyl group as shown in Fig. 2.

Fig. 2 – Effect of betaine on broiler performance

• Availability of cool water with increased number of waterers in which electrolytes (Potassium chloride, ammonium chloride or sodium bicarbonate) and ice cube prepared from chlorinated water can be added.
• Summer layer diet should have <250 mEq/kg dietary electrolyte balance (molar equivalence of Na+ + K+ – Cl-), whereas broiler diet like pre-starter, starter and finisher should have DEB values less than 220, 200 and 180 mEq/kg respectively.
• Use of Maduramycin as an anticoccidials in summer helps to increase water intake, whereas Nicarbazine and Monensin have negative impact.
• Mineral excretion increases during summer that’s why mineral premix dose need to increase 1.25% in feed formulation.

 Preventive treatment for heat stress through drinking water:

• During moderate hot weather – ascorbic acid (Vit C) 62.5 mg/L+ acetylsalicylic acid 62.5 mg/L + sodium bicarbonates 75 mg/L + potassium chloride 125 mg/L
• In heat stress- ascorbic acid (Vit C) 400 mg/ L + electrolytes + acetyl salicylic acid (disprin 1 tablet/5 L) + sodium bicarbonate 1gm/L

Conclusion

Heat stress is a major challenge in poultry production, which can lead to several health issues and production losses. Therefore, it is crucial to understand the causes and responses of birds to heat stress and implement appropriate mitigating strategies to minimize the adverse impact on production. Effective housing and nutritional management strategies can help reduce heat stress and improve poultry performance.Summer is an exigent season to chickens farming. Higher production performance and feed conversion efficiency in chickens directly proportional to the heat stress or more susceptible to heat stress. There is no single solution to hot weather problems and heat stress management requires a series of interventions. Installation of evaporative cooling system on farms, withdrawal of feed during hot part of day, provisions of fresh cool drinking water with vitamin C, electrolytes and sodium bicarbonate are important measures to be taken to minimize the major losses and increases the broiler and layer production at farms.Heat stress is a major challenge in poultry production, especially during the summer months. It occurs when birds face difficulty in achieving a balance between body heat produced and heat lost. This imbalance can lead to several health issues and production losses. Therefore, it is crucial to understand the causes and responses of birds to heat stress and implement appropriate mitigation strategies to minimize the adverse impact on production.There are several causes for heat production apart from the environmental heat. Some of them notably are higher feed intake, higher density feed and/or overcrowding of birds in a limited space, etc.

Compiled  & Shared by- Team, LITD (Livestock Institute of Training & Development)

Image-Courtesy-Google

Reference-On Request.