Heat stress in poultry

In many parts of India, summer is severe with maximum day temperature hovering around 40 C (ie 104 F). There is also shortage of water in summer and since water table goes down, bacterial count in water is high. It is therefore a challenging task to manage poultry in these conditions. During summer, weight gain, FCR, egg production, eggshell quality and hatchability are all adversely affected and mortality is high. Disease incidence is also more because of wet litter, immunosupression, vaccination failures and contamination of drinking water which are common in summer months. Hence in hot weather season, series of special measures in management, nutrition and medication have to be undertaken to minimize the losses.

Poultry birds are comfortable when environmental temperature is within the range of 65 to 75 F (18 to 24 C) This is known as comfort zone (zone of thermoneutrality) as birds do not suffer any ill effects of temperature changes, within this range. Weight -gain, FCR, Mortality and egg production are normal and birds maintain their normal body temperature (104 to 106 F). Chicks up to three weeks age require higher range of temperature

The upper and lower limits of comfort zone of temperature are called lower and upper critical temperatures respectively. When environmental temperature reaches beyond the range of comfort zone, bird tries to adapt and maintain normal body temperature by initiating physiological changes in its body .With extreme changes, in environmental temperatures the efforts for adaptation fail and birds suffer from cold or heat stress as the case be.

Cold stress:

As environmental temperature dips below lower critical level, cold sensory receptors in the skin are stimulated, pass impulses to thermoregulatory centre in hypothalamus and that signals contraction of peripheral blood vessels. Thus blood supply to skin is diminished and sensible heat loss through skin is prevented. At further lower temperatures birds will not be able to conserve heat any more and die due to cold stress

Heat stress:

With environmental temperature rising higher than upper critical limit, bird responds in the opposite way.

i) Peripheral blood circulation (to skin, upper respiratory tract, abdominal muscles. Combs and wattles) increases two to four times. Consequently blood flow to liver intestine, kidneys is reduced

ii) Birds start panting (increase in respiratory and heart rates)

iii) Birds stretch the body and take lying position closer to litter material and nearer to waterers fans.

iv) Water consumption increases by 1.2 to 3.2 times as per outside temperature.

The first three responses help in sensible heat loss and the last helps in internal cooling of the body system. However, with prolonged exposure to hot weather, these responses will lead to following harmful effects:

A) Reduced blood supply to visceral organs leads to

i) Poor Wt gain, higher FCR (due to impaired digestion,nd assimilation)

ii) Enteritis, reversal of body weight due to SIBO (Small intestinal bacterial over growth)

B) Acid base imbalance in the body: There is loss of CO2 because of continuous panting (hyper ventilation) Which results in increased blood pH (alkaloidosis). Kidneys act to restore the acid base balance by renal exchange of bicarbonates with Cl ion. This results in increased excretion of bicarbonates in urine and retention of Cl in plasma and that leads to systemic acidosis. Thus in heat stress initial alkaloidosis changes to systemic acidosis and birds die of acid shock.

In heat stress, supplementing diets with Ammonium chloride (NH4Cl) (0.3-1%) + Sodium bicarbonate (1-2%) is helpful, since Ammonium chloride reduces blood pH and Sodium bicarbonate prevents excessive acidosis.

Along with bicarbonates, electrolytes are also excreted in urine because bicarbonates are negatively charged, and Na an K ions (important electrolytes) being positively charged go with it. Loss of electrolytes affects the water balance.

C) Water imbalance in the body:

Normally Water intake + Water formed by oxidative metabolism in body

= Water loss through urine, faeces and respiration and evaporation

a) In heat stress water loss is more (60% more) through urine and increased respiration. This results in dehydration (decrease in extra cellular fluid level), fall in blood volume, fall in blood pressure and increase in plasma osmolality.

Body reacts to these changes by releasing Renin from kidney cells and that increases thirst. Anti diuretic hormone (vasopressin) is released from pituitary which reduces urine output by increasing water resorption in renal tubules.

Even though birds drink more water, its retention in cells is less because of loss of electrolytes and organic osmolytes (betain, Sorbitol Inositol) as stated above. Negative water balance, prevents internal cooling and hence there is further rise in body temperature.

Supplementation of Betain (osmolyte ) and electrolytes helps in maintaining water balance in the body cells against extra cellular osmotic gradients.

D) Immune suppression: In hot weather there is release of corticosteroids from adrenals and also depletion of plasma VitC. and reduction in lymphocyte count. The effect is immune suppression.

Tolerance to hot weather

Poultry can tolerate to some extent gradual change of season to summer, but if temperature shoots up suddenly on some days in between, it results in heavy mortality.

It is also reported that chicks exposed to higher brooding temperature during first few days, tolerate heat stress better in later life

Tolerance to heat stress is greatly influenced by Relative humidity in the air. High temperature and high RH form a deadly combination for poultry (Refer table below) Such conditions prevail in coastal regions of India during August to October months

Effect of Temperature and relative humidity on poultry

Temperature F C	Relative humidity	Effect on living conditions of poultry
68 to 78 F	20 to 26 C	Up to 40%	Optimum
78 to 86 F	26 to 30 C	40 - 75%	Harsh
86 to 104 F	30 to 40 C	Up to 45%	Progressively extreme
86 to 104F	30 to 40 C	65% and above	Impossible

Symptoms, Post mortem findings and diagnosis of Heat stress:-

When weather is moderately hot (75 to 80 F)( 24 to 26.7C) , paradoxically , FCR may improve as less energy is required for maintaining body temperature. As temperature rises above 80 F( 26.7 C) feed consumption starts declining. Drop in feed consumption is at the rate of 1.5% for every rise of 1C up to 30C and above that it is steep being 4 to 5% drop for every 1C rise.

FCR increases correspondingly.

At 90 F (32 C) and above birds are found panting continuously, drink more water, prostrate on litter extending the body and there is sudden and heavy mortality occurring in the later part of the day

In dead birds autolytic changes set in fast and in the post mortem examination of fresh carcasses, engorgement of subcutaneous capillaries, congestion of abdominal and breast muscles(cooked meat appearance), congestion of trachea, combs and wattles may be seen.

Diagnosis

In heat stress, intracellular calcium concentration increases which gives rise to efflux of Creatininekinase from cells to plasma. Elevation of plasma creatinine kinase is indicator of heat stress in chickens. But routinely laboratory tests are not necessary to diagnose heat stress condition.

Prevention of Heat stress in poultry

1) Providing ventilation with cool air

Well located and well laid out poultry 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. Care should be taken to avoid overcrowding and to provide shade to overhead water tanks and pipe system.

In extremely hot weather, however, the above measures are not sufficient and evaporative cooling systems -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 15C

Use of fans without evaporative cooling system may be harmful in extreme hot weather since it is only hot air that is blown in to the house.

2) Daily management to prevent heat stress :

In very hot season, the following measures are advised.

i) Feed withdrawal from 9am to 4.30 pm.: This is very effective in reducing heat stress mortality. Feed intake and digestion produce nearly 7% additional heat in the body which is maximum 4 to 5 hours after feed intake. This should not coincide with hottest part of the day (2 to 3 pm) Birds fasted in the day compensate intake in the night time and it should be seen that lights do not go off in night.

If biosecurity is poor, feed withdrawal may lead to coccidiosis, necrotic enteritis. Necessary medicines may be kept at hand in case such eventuality arises.

ii) Drinking Water: Cool Water (at 10-12 C) should be supplied continuously to birds. Watering space should be doubled. Over head tanks and pipe system should be properly covered to keep the water cool. Birds reject warm water and that accentuates heat stress.

Providing fresh cool water (5c) in noon time is very effective for internal cooling of body (heat sinks) and reducing symptoms of stress.

3) Preventive treatment through drinking water:

a) In moderate hot weather

Ascorbic acid....62.5 mg/litre

+ Acetylsalicylic acid 62.5 mg/litre

+ Sodium bi carbonate 75 mg/litre

+ Potassium chloride ( KCl) 125 mg/Litre

b) In heat stress

Vit C 400 mg/ L

+ Electrolytes

+ Acetyl salicylic acid ( Disprin 1 tablet/5 L)

+ Sodium bicarbonate 1gr/Litre.......may be used

4 ) Use of summer feed formula

In summer, feed should be made more dense with nutrients, Vitamins and minerals to compensate for reduced intake. Thus as the hot season progresses it may be necessary to fine tune feed formula again in mid summer In addition following features, which have bearing on heat stress control, should be included in summer feed formula:

a) Crude Proteins. Crude Protein level in feed should not be increased and protein from only vegetable source should be used. Proteins in general and those from animal sources in particular have higher heat increment values i.e. produce more internal heat in the body .

Secondly vegetable proteins (Soya, Sesame, Sun flower) are rich in Arginine. Under heat stress arginine absorption is low and that results in plasma aminoacid imbalance, leading to increased catabolism of amino acids adding to body heat Hence vegetable proteins are preferred in summer.

While keeping protein levels same, crucial amino acids may be increased to compensate for reduced feed intake.

b) Fats: fat should be increased by 2 to 3% at the cost of carbohydrates without changing 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

c) Vitamin C: Because of the release of corticosteroids in heat stress, there is increased demand for Vit C by adrenal glands for controlled production of hormones needed for gluconeogenesis. In heat stress there is also reduced synthesis and partial depletion of Vit C. Inclusion of Vit C at 150 - 200-400 Gr/ton of feed is recommended in summer months. If included in feed , there is no need to give ;in water again.

d) Sodium bi carbonate: It has positive effect of increasing water intake, and also reducing systemic acidosis. It can also be given through feed instead of through drinking water. In vegetarian feed, inclusion of Sodabicarb at 0.4% (4 kg/ton) + Sodium chloride0.25%( 2.5kg/ton) would properly balance sodium and chloride levels in feed.

e) Betain ( osmolyte) in feed

Betain (0.5 to 1 gr/ton) helps in maintaining water balance in the body cells against extra cellular osmotic gradient. Electrolytes also have similar action and are better given through water.

f) Anti oxidants: 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 more so of immune system VitE captures and neutralizes free radicals and its inclusion at 50 to 100 ppm in feed is advisable. Vitamin C also has antioxidant property. Similarly antioxidants namely BHA ,BHT and EQ will protect fats and oils in feed from oxidative rancidity .

g) Other recommendations:

i) Virginiamycin 15 to 20 ppm in feed apart from being growth promoter, reduces metabolic heat production, alleviates heat stress and stimulates immune responses.

j) Anticoccidials: Nicarbazine and Monensin are contraindicated in summer. The former decreases tolerance to heat and the latter depresses water intake.

k) Biotin supplementation at 150 micrograms /Kg feed is recommended.

l) Vit K supplementation is recommended particularly at time of debeaking or if there is threat of coccidiosis because in heat stress blood clotting time is prolonged.

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

Other associated problems in summer season

In summer season, apart from hot weather related ones, other associated problems could arise and following precautions are necessary to address them:

i) Regular sanitization of drinking water, periodic cleaning of water tanks and flushing pipe system. This is necessary since bacterial counts in water increases in summer due to water table going down.

ii) Use of Litter conditioner: In summer, since there is increased intake and excretion of water by birds there is wet litter and ammonia problems in poultry houses. Hence it is important to maintain litter dry.

iii) Vaccination: Strict cold chain should be maintained during transport storage and administration of vaccines. Vaccination should be carried out during cool hours.

v) Immunostimulants should be given for three days following each vaccination..

Summary :

Summer is a challenging season to poultry farming.There is no single solution to hot weather problems and series of measures are necessary to minimize losses due to heat stress. Among these following FOUR are important and would fairly ensure to preventmajor losses

1)Installation of evaporative cooling system on farms

2)Withdrawal of feed during hot part of day

3)Provision of fresh cool (5 c) drinkingwater with VitC,Electrolytes and Sodium bicarbonate in hot part of day

4)Use of summer feed formula