understanding and managing heat stress in poultry
TRANSCRIPT
Understanding and managing heat stress in
poultry Dr/ Hesham kotb
Alwadi broiler breeder veterinary supervisor KSA
D.V.M D.P.H
What is heat stress?
O Birds are ‘heat stressed’ if they have
difficulty achieving a balance between body
heat production and body heat loss.
O This can occur at all ages and in all types of
poultry.
O he body temperature of the broiler must
remain very close to 41 C (106F) body
temperature rises more than 4 C above this,
the bird will die.
O in hot weather, damp litter will make heat
stressed birds feel much more
uncomfortable than dry litter.
O In dry litter, birds will attempt to dust
bathe more readily to aid cooling.
O Turkeys, broilers and layers perform well in
comfortable summer temperatures between 70–
80oF (21-27oC).
O When ambient (surrounding) temperatures rise
above 80oF, feed intake, growth and production are
affected.
O Heat exhaustion and death will occur when
temperatures exceed 90oF (32oC)
O High humidity and high ambient temperatures are
extremely stressful for birds.
O If the amount of heat produced by a bird is greater
that the amount it loses, the bird’s body
temperature will increase.
O During hot weather birds will limit their daytime
activity and will reduce feed consumption or stop
eating.
O Feed consumption and digestion increases body
temperature, and thus birds will decrease their
feed intake to reduce their body heat production.
O Decreased feed intake will affect bird performance
and profitability. Water consumption will also
increase in hot weather, which will result in wetter
droppings and litter.
O In order to keep cool, birds will increase their
respiration rate as much as ten times the normal
rate and indulge in throat flutters or panting.
O Throat fluttering allows the evaporation of heat
by moving air in and out of the throat area
without actually entering the lungs.
O This method is very efficient on hot dry days,
but it is not very helpful during hot humid
weather because evaporation is more difficult.
O Older, heavier birds are less able to manage heat stress.
O Due to the lower body surface area per kilogram of body weight, older birds produce more internal heat and are less able to cool down by convection and evaporation.
O Older birds have more feathering and hence more insulation, which also makes it more difficult to get rid of body heat. In addition, as birds become larger there is less space between individuals in the poultry
O house, which traps more heat between birds and significantly increases the temperature at the floor level.
O Thus, air movement is an important method of keeping older flocks cool.
THE EFFECT OF HEAT STRESS ON EGG SHELL QUALITY
O Heat-stressed laying flocks often lay eggs with thinner, weaker
eggshells because of an acid/base disturbance occurring in the
blood as a result of panting (hyperventilation, Agular reflex).
O As birds hyperventilate to lose body heat, there is excessive loss of
CO2 gas from their lungs and blood. Lower CO2 in blood causes
blood pH to elevate or become more alkaline.
O This condition is called respiratory alkalosis. The higher blood pH
reduces the activity of the enzyme carbonic anhydrase, resulting in
reduced calcium and carbonate ions transferred from blood to the
shell gland (uterus).
O Increasing the amount of calcium in the diet will not correct this
problem. Another contributing factor to thin eggshells is reduced
intake of calcium as feed consumption drops, and an increased
loss of phosphorus
Visible signs of heat stress in poultry
O In general, birds will be suffering heat stress when any
of the following signs are evident:
O Gasping, panting, panting respiration - up to 250
breaths per minute - mediating evaporative cooling from
the surface of the lungs (80% of heat is lost this way)
O wings spreading
O Stupor, staggers and terminal convulsions.
O Slowness and lethargy.
O Increased cannibalism
O More Carcass down grades.
O Light body weight, poor colouring and
rough skin.
O Egg production drop for no apparent
reason
O Reduced egg size, poorer egg shell
quality
O Increased mortality
O Increased output of urine - further loss of
electrolytes
O Wet droppings develop
O Thirst increases- many times
O Bone metabolism is disturbed e.g. tibial
dyschondroplasia
O Ascites incidence increases
Invisible signs of heat stress in poultry
O pH of blood plasma rises
O pH within the cells falls
O Urine output increases and so does
electrolytes
O Bicarbonate (HCO3) is lost
O Stress hormones appear in the blood
O Gene function is disturbed
O Resources being diverted to unproductive
efforts by the animal (bird) to restore balance
(homeostasis)
O Heat shock proteins are activated to shut down
metabolic reactions and to protect heat-
sensitive tissues.
O Responses to intercurrent diseases or
pathogens decline rapidly.
O All production is stopped due to loss of
homeostasis
PM Picture O Congestion and build up of fluids and blood is common.
Lesions are often present.
O Color changes to a pale yellow and is congested
O Kidney : Swells and is inflamed, water blood and urine
accumulates.
O Muscles are dry and sticky to touch.
O Blood is thicker and darker than normal.
O Crop and gizzard are empty and dry.
O Gizzard lining peels off easily
Physiological heat stress adaptation
O Flocks not previously acclimated to high temperatures typically suffer the greatest loss
O Young birds exposed to high environmental temperatures are more thermo tolerant later in life, due to the production of heat shock proteins.
O The best method of cooling during periods of lower humidity is evaporative cooling (fogger, mister or cool pad).
How do birds respond to increasing temperature?
O Birds will try to re-establish their heat
balance with the surrounding by changing
their normal behaviour. Birds may:
O ● Try to move away from other birds.
O ● Move against cooler surfaces, such as the
block walls or into moving air streams.
O ● Lift their wings away from their bodies to
reduce insulation and expose any areas of
skin that have no feathers.
O ● Elect to pant slowly.
O ● Rest to reduce heat generated by activity.
O ● Reduce feed intake.
O ● Increase water consumption.
O ● Divert blood from internal organs to the skin,
which darkens skin colour.
O ● Begin fast pantingHigh relative humidity
reduces the effectiveness of evaporative heat
loss.
Can poultry acclimatise to high temperatures?
O Adult birds take about five days to acclimatise to high
temperatures. Birds are more susceptible to sudden,
large changes in temperature.
O The first very hot days after a cool spring often result in
increased incidence of heat stress.
O Some of this will be due to poor acclimatization, but
some will be due to managers being less well prepared
than later in the summer.
What are the key features of housing that protect birds from hot
weather?
OThe key features are:
O● Insulation
O● House design and location
O● Ventilation
What does insulation do?
O Insulation greatly reduces heat transfer through a wall
or roof. Even on a normal summer’s day, it is surprising
how much solar heat can penetrate a roof if the
insulations deficient.
O On a hot day, the surface of a roof can reach 600C.
Measurements have shown solar gains of up to 30
Watts per square metre (W/m2) coming through old
broiler house roofs.
O The heat is radiated from the ceiling into the house,
increasing the heat load on the birds below.
What is the recommended standard for insulation?
O The effectiveness of insulation is described by the ‘U value’ (the lower the number the better).
O The modern recommended standard U value is: ● U = 0.4 W/m2 / 0C or better.
O In new, clear span buildings, the roof space can accommodate extra insulating material, and the walls are made using composite panels.
O The U value is typically 0.35
O The design of the building and its
ventilation system, the siting of new
buildings and construction materials, will
all have an effect. Roof colour, reflectivity,
pitch and orientation, and whether the
building is in the shade or not, are also
factors which will have a small bearing on
solar heat gain.
O Expert advice should be sought at the
design stage
OThe inlet system – Whatever the air
change capacity available, it is critical
to distribute air uniformly and at high
speed to all of the birds in hot
weather. This is particularly true for
birds finishing in the meat sector and
where there are high stocking rates.
What are the benefits of high airspeed over birds?
O High air speed is essential in heat stress relief. In
systems with lower stocking rates, the effects are
greater.
O ● Ensure that air passing over the birds from the inlets
is as near to outside temperature and humidity as
possible.
O ● Remove the boundary layer of hot air around the
birds, aiding convectional heat loss.
O This is vital when birds are at, or near, peak stocking
rate
O ● Remove humid air from around the birds’ heads,
making panting more efficient.
O ● Imparts a sense of windchill to the birds. This makes
birds feel cooler than the actual temperature.
O Birds in one house might stop panting when in an
identical house, at the same temperature but with
slower airspeeds, the birds keep panting.
O ● Makes the most of evaporative heat loss when, at
very high temperatures (> 32 C),
O the effects of windchill diminish
What are the recommended air speeds over birds in hot weather?
O All meat producers should aim for between 1 m/s and
3 m/s for relief against extreme heat.
O 1 m/s should be an absolute minimum for
commercially stocked houses.
O 1.0 -1.5 m/s should be within the abilities of most
conventional powered ventilation systems, especially
after minor upgrades. (1m/s = 200 ft/min)
O To achieve 1.5 – 3 m/s, the house would usually need
to be operating in a tunnel ventilation format.
Can I use internal recirculation fans if air speeds are inadequate?
O Internal recirculation fans can play an important role where air speeds over birds are poor.
O It is important to distinguish between recirculation fans, which do not change air, and the main ventilation fans that do.
O However:
O ● The air movement generated is at house temperature and humidity.
O ● Air distribution is uneven and birds sometimes huddle into the discharge air plume, increasing stocking rate under the fans.
O ● Always consider the possibility of modifying the inlets to increase air speed evenly – this might also require an increase in air change capacity.
the disadvantages of evaporative cooling
O The disadvantages are that:
O ● In extremes of very high temperatures and very high humidities, cooling systems
O might be ineffective or detrimental.
O ● There is about a 4.5% RH increase for every 1 C of cooling. A water supply that
O reduces temperature by 6 C must increase % RH by about 27%. Managers should
be aware that it is common for the house humidity probe not to accurately reflect
this dramatic humidity increase.
O ● Should cooling not prevent heavy panting, the resultant increase in % RH can
reduce panting efficiency and increase the risk of heat stress.
O ● A cooling system cannot replace the need for high air speeds from the existing
O ventilation system.
O ● Incorrect positioning of nozzles can result in poor cooling and wetting of litter.
O ● They require frequent maintenance, especially in hard water areas.
O ● There is limited expertise or cost benefit information available.
Does reducing feed intake or feed removal help in heat stress relief?
O Birds in hot environments reduce feed consumption
naturally, reducing heat from metabolism. Feed
conversion efficiency and growth rate is also reduced.
O Techniques that increase activity or stimulate food
consumption may be counterproductive.
O Feed removal prior to the hottest part of the day has
been shown to be beneficial in reducing mortality.
O The advantages are reduced metabolic heat output, and
where feeds systems can be lifted, increased floor
space and improved air distribution over the floor.
Why is fasting benefcial during heat stress?
O In addition to heat-stress mortality, economic losses associated with broiler heat stress also occur as a result of lowered growth rate and decreased feed efciency. Terefore, it is natural for producers to want to stimulate feed consumption in hot weather. However,
O any management technique which promotes feed consumption or increased activity during the peak hot periods may be counterproductive.
O The extra feed consumed will increase the bird’s heat load and probably result in additional mortality.
O Fasting the broiler prior to or during peak hot periods of the day lessens the heat load and enhances survival.
O Fasting reduces the heat production from digestion,
absorption and metabolism of nutrients.
O Fasting also has a calming effect. Movement in animals
occurs through muscle contraction which generates
heat. In hot environments this heat production only
adds to the heat load. Therefore, to lessen the heat
load, broilers should be kept as calm as possible.
O This is especially important during the hottest parts of
the day. Once the hottest periods are over and ambient
temperature starts to fall, the broilers will usually begin
consuming feed again.
Can cool water alleviate heat stress?
OWater is lost from the lungs when
birds pant and so more water needs
to be drunk to prevent dehydration.
OCool water stimulates water intake.
Reducing the body temperature of
the bird is beneficial and has been
associated with reduced mortality.
In Summary: O ● Provide adequate ventilation for the number of birds
housed.
O ● Provide fast air speed over birds.
O ● High humidity increases the likelihood of heat stress in hot weather.
O ● Where possible, reduce stocking densities during hot weather both in the shed and during transport.
O ● Regularly maintain and test alarms and emergency ventilation equipment.
O ● Make contingency plans in advance so all know their respective roles and ensure that someone is available with authority to take actions.
Results of electrolytes
O some researchers have attributed the increased
survival rates of heat stressed broilers receiving
supplemental salts such as protassium bicarbonate,
potassium chloride, sodium chloride and ammonium
chloride to the increased water consumption which
results, not to the salts
SUPPLEMENTS (MINERALS AND VITAMINS)
O Imbalances in acid-base balance occur in heat stressed birds. Therefore, inclusion of various compounds in the diet or water is a common practice to alleviate the adverse effects of heat stress.
O These include sodium bicarbonate (NaHCO3), potassium chloride (KCl), calcium chloride (CaCl2), ammonium chloride (NH4Cl) and vitamin C (ascorbic acid).
O Sodium zeolite and aspirin are also beneficial in reducing the effects of heat stress
O in laying hens
O Suppression of growth can be partially alleviated by
supplementation of
O 1% NH4Cl 0.15% - 0.6% KCl 0.2% NaHCO
O 3. Supplementation of probiotic lactobacillus strains may enrich
diversity of micro flora in chicken.
O • The addition of NaHCO3 and KCl to feed or drinking water
reduces negative effects of heat stress.
O • The addition of vitamin C to drinking water or feed helps to
reduce corticosterone levels during heat stress.
O • Aspirin also decreases corticosterone levels and can be used
when allowed by legislation.
O • Betaine results in an improved performance during heat stress.
O • Although litter quality is usually not an issue during summer, it is
advised to use products that improve gut barrier function / reduce
intestinal bacterial activity (e.g. strong anti-oxidants, butyrate,
medium chain fatty acids).
O Vitamin C
O Under heat stress, birds are not able to synthesize
the sufficient amount
O of vitamin C.
O Vit C @ 1000mg/kg Supplementation of ascorbic
acid.
O Heat resistance Carcass quality.
O Carcass weight. Carcass CP content.
O Act as antioxidant reduce oxidative injuries.
O Reduce mortality.
Electrolytes & others reduce
heat stress
NH4Cl
CaCl2
Betaine
KCl
NaHCO3
Sodium zeolite
Aspirin
vitamin C
A- DRINKER SYSTEM MANAGEMENT OF THE HEAT-STRESSED FLOCK
O 1- Ensure that drinkers have suffcient water flow (>
70 ml/minute/nipple drinker)..
O 2- Cooler water will help reduce the birds’ core
temperature and thus reduce the impact of heat
stress.(may add ice to water)
O 3- Cooling drinking water by flushing water lines
during the afternoon has been shown to increase
feed consumption and sustain egg production in
heat-stressed layers.
O 4- Keeping water below 25°C will help maintain higher
water intakes and therefore encourage higher feed
intake. Water temperature above 30°C will negatively
impact water intake and have further negative impact
on feed intake.
O 5- Use vitamin and electrolyte supplements in the
drinking water to replenish the loss of sodium, chloride,
potassium and bicarbonate in the urine. Electrolyte
supplements are best used in anticipation of a rapid
rise in environmental temperature.
O 6- In case chlorinated water is being used in the farm, it
is recommended to discontinue chlorination on
extremely hot days may use a substitute as H2O2.
O • Bacteria grow much more rapidly in the water
lines during hot weather. It is very important to
do whatever possible to guarantee water
sanitation (i.e. oxidation reduction potential of
greater than 700 mv).
O • Dump drinkers and flush water lines as often
as possible during hot weather to ensure water
is consistently as cool as possible.
B- MANAGEMENT OF THE HEAT-STRESSED FLOCK
O Avoid excessive activity during the hottest part of the
day.
O The hot weather is a great stress on the birds, so avoid
bothering and disturbing the birds during periods of peak
heat.
O 1 - Do not disturb the birds during the hottest time of the
day (afternoon and early evening).
O Adjust work schedules and lighting programs so that
routine work is done early in the morning or at night.
O 2- Management practices that require bird handling,
such as beak trimming, transfer and vaccinations (by
eye drop, wing web or injection), should be done in the
early morning hours.
O 3- Using roof sprinklers during times of extremely high
temperature can remove heat from the roof and cool the
inside of the house.
O 4- Do not run the feeders during the hottest time of the
day
O 5-Adjust fan thermostats so all fans run continuously
during the night and early morning hours. The goal is to
maximize nighttime cooling in the house to prolong the
period of moderate temperatures the next morning.
C- LIGHTING PROGRAMS FOR HEAT-STRESSED FLOCKS
O 1- Adjust the lighting program to provide more morning light hours (and fewer afternoon light hours) to encourage feed consumption during the cooler period of the day.
O 2- Use a midnight feeding of 1–2 hours to provide an additional feeding during the cool of the night to encourage feed intake during hot weather ( in layers).
O 3- In extreme heat stress, lower the intensity of light during the hottest time of the day to reduce bird activity.
O 4- Intermittent lighting programs have also been used successfully in heat stress conditions to encourage feed intake.
D- When formulating the diet for hot weather condition
O Including oil in the diet has long proved to be beneficiary in hot climates and shows better effects than in moderate climates. For example, the inclusion of oil increased feed intake by 17.2% at 31°C compared to only 4.5% at temperatures of 10-18°C.Digestion of fat produces less heat than the digestion of carbohydrates and proteins.
O Oil binds the fine particles in the feed and stimulates feed intake. Additionally, it increases the energy level in the feed, which is very important to compensate the reduced energy intake due to less feed intake during the hotter periods.
O Fat has also been shown to slow down feed passage through the gastro-intestinal tract, and therefore increases nutrient utilization. Up to 5% oil can be used. An additional
O advantage of oil is the content of linoleic acid, which improves the production and weight of the eggs.
O Poultry prefer high energy (in terms of fat calories) and low protein (2- 3 percent less than normal) diets with balanced amino acids (in terms of lysine and methionine).
O Replace 10-15 percent of feed energy normally supplied by carbohydrates and proteins with 1-2 percent vegetable oil/fats.
O Substitute 20-25 percent of de-oiled rice bran with oiled rice bran. This will not only
O ensure that the feed is rich in fat calories, but it will also prevent feed becoming dusty so making it more palatable.
O Use only fresh oiled rice bran, and keep only 1 week to 10 days’ supply to avoid oxidation of stocks.
O Supplement the layer feed with amino acids in line with feed intake. Replace DL methionine with methionine hydroxyl analogue and betaine.
O Increase the calcium content of the diet from 4 percent to 5 percent.
O Replace 40-50 percent of any salt in the diet with sodium bicarbonate to help maintain egg shell quality.
O Supplementation with additives such as synbiotics,
phytobiotics, acidifiers and dextrose can also help in
alleviating the heat stress.
O there are several things to consider:
O 1-Formulate diets using highly digestible materials,
particularly protein sources.
O Metabolism of excess protein is particularly heat-
loading on the bird and exacerbates the ionic
misbalance.
O Formulate to digestible amino acid targets and do not
apply a high crude protein minimum in the formula.
O Synthetic amino acids can reduce crude protein in the
diet without limiting amino acid levels.
O 2-Increasing the proportion of energy
contribution from highly digestible lipid,
rather than starches or proteins, will
reduce the body heat production resulting
from digestion. This is known as heat
increment and is lowest with the digestion
of dietary fat.
O 3-The phosphorous requirement
increases during heat stress. Increases of
up to 5% should be appropriate under
heat stress conditions.
O 4- The ratio of chloride to sodium in the diet should
be between 1:1 and 1.1:1 in hot weather
conditions, with a target dietary electrolyte balance
(molar equivalence of Na+ + K+ – Cl-) of about 250
mEq/kg. Due to elevated electrolyte loss in hot
weather,
O Higher sodium levels may be required (0.02–0.03
% more than in non-heat stress conditions).
O Care should also be given that water is not
providing a significant level of chloride to the birds.
O 5- Increase the digestible lysine (and other amino
acids) to energy ratio with 5 to 10 % in heat-
stressed birds.
O 6- Due to the reduced feed intake E vitamin and
trace mineral intake is also reduced, so Vitamin
and mineral premixes should be increased by 25
percent, with particular attention paid to vitamins
C, A and.
O Many of these micro nutrients, particularly B
vitamins and antioxidants, may be beneficial to the
bird in heat stress conditions.
O Vitamin C at 200-300 mg/kg of diet can be added
to the diet to improve performance.
O 7-Organic zinc may improve shell quality by
assisting the activity of the carbonic anhydrase
enzyme, as zinc is a key mineral element of this
critical enzyme.
O 8- Organic copper may also be helpful, by
reducing the negative antagonism between
inorganic copper and zinc sources during
digestion.
O 9- Do not use nicarbazin (anticoccidial drug) during hot
weather, as it can increase heat stress induced
mortality.
Nutritional strategies for heat stress
Reduce fiber
content phosphorou
s requirement
increases
Replace carbohydrates
for oil
reduce crude protein
Higher Na levels (0.02-0.03)
Organic zinc
Water CL lysine
Organic copper
Antioxidants
Vit E
B vitamins
Vitamin C
no nicarbazin
E-HOUSING CONSIDERATIONS DURING HEAT STRESS
O Evaporative Cooling Sprinklers are commonly found in turkey barns for evaporative cooling, which are used when temperatures are more than 79-86oF (26-30oC) and the barn air is very dry.
O Too much water can actually increase the humidity of the barn to dangerous levels.
O Remember, high temperatures and high humidity make heat dissipation by evaporation very difficult.
O Death due to heat exhaustion will occur more quickly if both temperature and humidity are high.
O The ventilation system should be checked to insure efficient operation prior to the arrival of the hot season.
O 1- Clean and ensure function of fan louvers.
O 2-Fan belts should be tightened or changed to avoid slipping or breaking during periods of high temperature.
O 3- Remove light traps during production period to increase fan capacity to maximum
O 4-Air inlets must be adequate to supply the airflow needed to ventilate the house during warm weather. Inadequate inlet space will throttle down the fans and decrease airflow.
O Inlets should be kept clean and free of anything that might restrict the flow of incoming air. Use baffle boards to direct incoming air onto the birds.
O 4-Thermostats should be checked for accuracy. An auxiliary power system must be in place in case of a power outage during hot weather.
O 5- In houses equipped with evaporative cooling systems,
the pads should be cleaned or replaced when they
become clogged.
O Water flow over the pads should be uniform with no dry
areas. Air will flow preferentially through dry areas since
there is less resistance.
O 6-Check the water filters and change if necessary. A
clogged water filter restricts the flow of fresh drinking
water into the house.
O 7-Clean spider webs and dust from window screens
frequently to improve ventilation inside the house.
O 8-Roof reflectivity can be increased by cleaning and painting
the surface with metallic zinc paint or by installing an
aluminum roof
O • Plastic or wooden baffles should be used to force the
moving air downward to ensure that the birds receive the
maximum advantage.
O • Make sure fan belts are tight. A loose belt can reduce fan
efficiency by 30 percent or more.
O • Replace old fan belts. If the sides of the fan belt are worn,
the belt will tend to ride lower in the fan and motor pulleys,
decreasing the speed at which the fan rotates.
O A reduction in fan speed of 10 percent will decrease the
airflow by 10 percent.
O Shutters and/or screens on air inlets need to be cleaned
daily or as required to allow maximum flow of air.
Heat stress management through DEB
O Heat Stress Management is directed at the reduction of wasted production. An estimation of the deviation from the desirable value for the equation [Na+ + K+] - [Cl- + S=] may be made from the knowledge of the composition of the ration.
O Supplementation of electrolytes via the drinking water or feed can then be made to restore the ionic situation to the desired levels.
O There are a number of factors which may complicate the picture. Such as:
O 1- The majority of added phosphate in feeds is acidogenic.
O 2 - The chloride salts of many added vitamins and amino acids also distort the formula's positive value.
O 3 - the natural variation of K+ ( Potassium) in the feed may be quite large (and this is a Key Electrolyte).
O Concurrent medications might influence the balances.
Dietary Electrolyte Balance O The dietary electrolyte balance (DEB), also known as
acid-base balance is probably more critical at high temperature than at normal temperature, and different results have been reported on the most appropriate DEB for birds under high temperature conditions. Very high (360mEq/kg) and very low (0mEq/Kg) DEB can result in metabolic alkalosis and acidosis, respectively. Very high and low DEB should be avoided during diet formulation The birds under heat stress will perform best at a DEB of 250 mEq/Kg (Ahmad and Sarwar, 2006)
F- REARING CONSIDERATIONS TO COUNTER ACT HEAT STRESS
O Early heat conditioning (EHC) seems to be one of the
promising methods in enhancing heat resistance of
broiler chickens.
O Early heat conditioning refers to the practice exposing
broiler chicks to high temperature (36°C) for 24 h at 3
to 5 d of age (Lin et al., 2006). Where possible, and in
particular in older broiler houses with less efficient
ventilation, it is sound practice to reduce stocking
densities in the summer Several nutritionists
recommend
O the administration of 1g ascorbic acid/liter drinking
water throughout heat periods
O The detrimental effect of heat stress on egg production
can also be alleviated by dietary supplementation of
Vitamin A (8000 IU/kg diet)
O Vitamin E supplementation is beneficial to the egg
production of hens at high temperatures and is
associated with an increase in feed intake and yolk and
albumen solids
O Heat stress could induce the unfavorable changes in
indigenous bacterial micro biota
O The supplementation of probiotic Lactobacillus strains
may aid in restoring the gut microbial balance of
chicken having suffered heat stress .
OReduce the thickness of the old
built-up litter. Two inches of
fresh litter may be provided in
the place of old litter.