Poultry farming is very profitable business
if done on modern and scientific basis by
maintaining health and production of poultry
birds and by protecting poultry flocks
against extreme hot summer season in
Pakistan. Birds are warm blooded living
creatures and maintain body temperature
through out the year. Heat is produced
inside the body of bird as a result of
metabolic processes. Excess heat is
dissipated to the surrounding environment to
maintain body temperature and avoid over
heating. When the heat produced by the bird
is not dissipated to the surrounding
environment or when the heat produced is
more than dissipated, the body temperature
of bird increases resulting heat stress in
poultry flocks. Similarly, birds are heat
stressed if they feel difficulty in
achieving a balance between body heat
production and heat lost. When equilibrium
is disturbed in the body between heat
production and heat loss, less heat loss and
more produced within the body of bird
results heat stress. The summer weather and
high environmental temperatures are the
factors responsible for heat stress in
poultry flocks. During the summer season the
temperature of the poultry house should be
decreased enough so that birds feel
comfortable in losing their body heat to the
external environment. Poultry farmers should
be conscious and vigilant about maintaining
environmental temperature according to
requirement of the birds especially during
the summer. The adult chicken body
temperature varies between 105–107°F
(40.6–41.7°C) and average body temperature
of newly hatched chick is about 103.5°F
(39.7°C). For maximum production performance
of the poultry flock the body temperature of
a bird must remain within narrow limits of
106°F (41°C). Certain physiological
conditions cause variations in body
temperatures among birds. Like, male birds
have high body temperature than females
because of higher metabolic rate and more
muscular activity. Physiological activity
and increased mobility increases the body
temperature in both male and female birds.
Heat loss from the body occurs through
radiation, conduction, convection and
panting in birds. The radiation is the
process through which the heat loss occurs
from the body of bird to the environment
through the variation in temperature of body
and environment, the more the temperature
difference more will be the heat lost from
the surface of body. Temperature loss
through convection occurs through movement
of air inside the poultry houses, and when
the temperature of surrounding air is higher
than the temperature of body, heat loss
reduces very much and may fail completely
through the process of convection.
Conduction is the direct touch of the body
of bird to the cool objects inside the
poultry house. Panting is the process
through which heat is lost through vapors
during respiration by exhaling the moist
air. The birds have no sweat glands and most
of the heat loss occurs through respiratory
route. The respiratory tract of birds is
moist and during respiration the vapors come
out and evaporate along with excessive heat
resulting in the lowering of body
temperature. The water vapors may not
evaporate form the respiratory tract due to
high level of humidity in the atmosphere. If
the humidity is more the heat loss will not
occur and the internal body temperature will
increase. Some degree of body heat is also
lost through the fecal excretion. Heat
stress can be acute or chronic. Short and
sudden periods of extremely high temperature
and humidity result in acute heat stress.
Extended period of elevated temperature
along with increased humidity results in
chronic heat stress.
Sign and Symptoms of Heat Stress in Poultry
Flocks:
When environmental temperature increases in
poultry shed the main indicator is prolonged
panting. Slow panting is normal activity
during summer in birds but prolong panting
is the result of heat stress. Rasping,
dullness, increased heart rate, congestion
of mucous membranes, dehydration, elevation
of body temperature, staggering, trembling,
convulsions, slowness and lethargy,
cannibalism and dyspnoea. Body weight gain,
Feed Conversion Rate (F.C.R), egg
production, growth rate, egg size, egg
quality and fertility will be decreased in
layer and breeder flocks. The birds will
stretch their feathers outwards to give
maximum exposure to the surface of skin for
dissipation of heat to the external
environment. The panting requires muscle
activity in birds will result in excessive
heat production inside the body of bird. The
respiration rate can increase up to 10
times. Increased respiration rate causes
more loss of Carbon-dioxide (CO2) from body
resulting in rise in plasma pH, and will
result in respiratory alkalosis. The
concentrations of Sodium (Na+) and Chloride
(Cl–) ions in blood will increase and
Potassium (K+) and Phosphates (PO4++) will
be reduced. The birds will try to find the
‘comfort zones’ inside the house and will
stick to cooler objects inside the sheds,
take shelter under feeders, attach drinking
water troughs and containers, attach the
walls of the sheds, sit on litter, stretch
their necks high and will try to take bath
in the litter. There will be restricted
movement or birds may show no movement with
the symptoms of depression. Diarrhea results
in the loss of electrolytes, legs become dry
and blood thicker. The electrolyte intake in
feed is also reduced because no intake of
feed. Some degree of mortality can also be
seen inside the poultry shed with the
following post mortem changes like, dry and
sticky muscles with cooked appearance, blood
thick in consistency, shriveled and dry
legs. Petechial hemorrhages are found on the
mucous membrane, abdominal fat, liver, heart
and skin. Hyperemia and congestion of
respiratory tract along with congestion of
lungs, blood vessels and brain can be seen.
Glue like contents can be seen in intestine
with empty crop and gizzard. Dilatation of
right side of the heart is also observed.
Rigor mortis sets and goes early.
Putrefaction is also rapid in dead birds.
Effect of Heat Stress on Health and
Production of Poultry Birds:
Above the temperature of 20°C with 1°C
increase in temperature 1.5 % feed intake
decreases but water intake remains normal.
Water requirement increases above the
temperature of 30°C and lead to diarrhea
because of reduced feed intake. With 1°C
increase of body temperature, 20-30% of
metabolic rate increases thus heat
production increases and the normal
temperature of bird increases form 42°C to
44°C. At this stage water intake and
metabolic rate of body increase very much,
but reduced feed intake leads to wet
dropping and diarrhea. Naturally birds
decrease intake of feed during hot
environment to reduce heat production from
metabolism. Decreased feed intake leads to
the production of thin shelled, cracked and
poor quality eggs. Birds during production
stage are already under stress and easily
become susceptible to heat stress. When
respiration increases, panting increases,
CO2 level increases and affects on Central
Nervous System (CNS) resulting convulsions
and death. With long periods of high
environmental temperature the fertility and
hatchability of eggs is reduced.
Effect of increasing Temperature on health
and production of poultry birds
TemperatureEffect on Health and Production
of Birds
65 – 80 °FBirds enjoy temperature less than
75°F but also feel comfortable and function
normally up to 80°F.
81 – 85 °FFeed consumption drops while water
intake increases. Feed Conversion Ratio (FCR)
and weight gain decreases in broiler birds.
Egg production drops in layer and breeder
flocks.
86 – 95 °FEgg production, egg shell quality
and fertility rate in breeder / layer flocks
decrease significantly. Feed consumption and
FCR are also reduced in broiler and layers.
96 – 100 °FSome degree of mortality, marked
depression, nervous signs along with
symptoms of trembling, staggering, and
convulsions can be seen in poultry birds.
101°F & AboveThe temperature above 101°F is
referred to as “Lethal Temperature”. Severe
stress results shock and death in birds at
this temperature.
Management of Heat Stress in Poultry Flocks:
The primary objective of heat stress
management is to ensure maximum heat loss
from the house in order to lower the
temperature of the house. For this purpose
following points can be kept in mind during
running a poultry flock.
1. The direction of building of poultry
sheds should be from East to West in length
and North to South in width in the plain and
warm areas under Pakistani climatic
conditions. It is advisable to provide flow
of wind from the North and South sides and
to avoid poultry birds from maximum exposure
of hot sunlight during the day from the
sides, the longitudinal direction of shed
should be made from East to West.
2. Evaporative cooling system can be used
inside the shed through cooling pads and
from using the sprinklers at those farms
where environmental temperatures are high
while humidity level is low. The excessive
heat is lost during evaporation of water and
cool air is produced inside the shed, the
resultant humidity produced should be
monitored efficiently. There is about 4.5%
RH increase for every 1°C decrease of
temperature through evaporative cooling.
3. Vegetation should not be done along the
sides of poultry house. The trees, crops and
vegetables along the poultry house decrease
flow of wind across the shed and increase
stress on the birds. The vegetating lands
often remain irrigated during summer and
increase the humidity level in the
surrounding environment, thus making the
situation more adverse.
4. It has been estimated that about 60% of
the heat inside the poultry shed comes from
the roof. The roof of the poultry shed can
be made steeper and high. Water sprinkling
in high temperature can be done to make roof
cool. Furthermore, an insulated house is
necessary for maintaining internal
temperature of the poultry house.
5. Electrolyte therapy should be done to
balance salts. Vitamins and minerals can be
added in the feed. Vitamin C can be given in
the feed or in water for the regulation of
body temperature of the birds. Protein
metabolism produces more heat production
than fats and carbohydrates. The protein to
energy ratio should be readjusted.
6. The temperature requirement of broiler
birds based on age of birds should be
monitored. The Day Old Chicks (DOC) and
early aged growing broiler chicks require
more temperature compared to adult ones. The
environmental temperature should be
decreased with increasing age of birds.
7. Litter should be dry and not be much wet.
The dry litter indicates the excessive heat
and decreased humidity, the wet litter
during summer is indicative of increased
humidity inside the poultry house. The wet
litter after drying will form cakes and
stick to the floor. Bad smell and ammonia
will be produced inside the house from wet
litter will hamper the growth rate, attract
flies and increase the stress upon birds.
8. Stagnant air inside the shed can be
circulated to maximize heat loss by
convection. Internal re-circulation fans can
be used for even distribution of air inside
the house. Exhaust fans can also be used for
expulsion of hot air from the poultry house.
The distance between the sheds should be
adjusted in this way that the flow of wind
across the sheds is not interrupted and
fresh air is available to the flocks.
9. Water supply to the poultry flock should
be clean and cool. The temperature of
drinking water should not be more than 20°C.
During summer season water consumption is
increased and helps in reducing body
temperature of bird. The number of drinkers
and space should be increased and supply of
more water should be ensured to prevent
dehydration in birds. On an average for each
1gm of feed intake birds consume 2–3mL of
drinking water during winter to 4–5mL of
drinking water.
10. The feeding to poultry birds should be
done during the cool hours of the day i.e.
during the early hours in the morning and
during late hours in the evening. Feeding
during hot part of the day should be
avoided. Feed conversion, metabolic and
growth rates are reduced due to depriving
feed to birds, but this method is beneficial
in reducing mortality in birds due to heat
stress.
11. The stocking density should be decreased
during summer. High stocking density will
result in ventilation failure. The increased
metabolic rate of birds during summer
increases heat production inside the poultry
house and decreased loss of heat during hot
and humid weather will increase overall
temperature of the poultry house. The
stocking densities should be adjusted
according to temperature and humidity
conditions in the respective area.
12. Special care should be taken during
loading and transporting of birds.
Transportation of birds should be done
during cooler parts of the days especially
during morning, evening or in the night. The
transportation of birds during hot weather
may be done in off-feed birds in unavoidable
circumstances.
13. The overall general health conditions of
the poultry birds should be maintained. In
this regard timely diagnosis of diseases and
prompt treatment of diseased birds should be
ensured. The layer and breeder flocks should
be regularly screened for Mycoplasmosis,
Salmonellosis Avian Influenza (A.I) and New
Castle Disease (N.D) through serological
examinations.
Efficient heat stress management during
summer season in poultry flocks can increase
profitability of poultry business. The
increased egg and poultry meat production
during summer season can be helpful in
fulfilling the protein requirement of the
general public. Increased egg and meat
production can also overcome the crisis of
food shortage in the country.
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