Hot and bothered. Devon-based poultry vet Ben

Pig_Summer14_p16-17:FB_0606_p12-13_Marketing.qxd 06/06/2014 13:01 Page 16
POULTRY HEALTH
Hot and
bothered
Devon-based poultry vet Ben Crisp (BVSc MRCVS) says that while warm and
dry weather is, theoretically, good for both humans and poultry, excessively
warm days can take their toll on broilers and laying birds
Chickens are designed to be able to
produce and lose heat easily and
with little effort between set ambient temperatures. Once the ambient temperature and, therefore, the
temperature of the bird rises above
the ‘upper critical limit’ then the
bird has to actively lose heat via
open mouth breathing.
Eventually, however, excessive
open mouth breathing leads to
more heat being produced than
the heat that is lost. At this critical
turning point the bird is under
‘acute heat stress’ and should this
continue the bird then becomes
‘chronically heat stressed’.
While temperatures above 27°C
or relative humidity above 50%
are enough to cause panting, the
negative effects of heat stress can
be seen at temperatures above
24°C. However it must be remembered that this will vary depending
on the age of birds and the relative
humidity.
release of heat shock proteins.
Their function is to shut down
metabolic reactions to protect vital
organs.
Post-mortem findings usually
include congested carcases, varying in severity, depending upon
how long birds have been heat
stressed for. Generally the carcases
are dry and tacky to the touch.
Blood is darker and thicker than
usual. There may be a mucoid exudate found in nostrils or mouth,
again depending upon the severity
of heat stress.
The effects of elevated temperatures on poultry
“Encourage
birds to drink
and provide
electrolytes in the
drinking water”
When temperatures rise above
43°C birds are at risk of hyperthermia and death if immediate action
is not taken. It is worth noting
that a sudden increase in environmental temperature, typically
above 5°C, can induce acute signs
of heat stress even with relatively
low overall temperatures. The
broiler can adapt to higher temperatures, but it takes about five
days for this to occur.
HEAT-STRESS SIGNS
Visible signs of heat stress include
panting, a gradual or spike in
water consumption and a reduced
16
feed intake as the birds try to limit
their movements around the shed.
In a layer environment, egg production can acutely reduce. Birds
will often stretch out their wings
and legs in an attempt to increase
their surface area and aid heat
reduction.
There are also a number of
invisible signs that can have a neg-
ative effect on the bird. The pH of
blood plasma rises while the pH of
cells falls. The urine output of the
bird will increase and, with this, so
does the quantity of electrolytes.
The birds’ resources are being
diverted to heat loss and so production, whether it be weight or
eggs, will be negatively affected.
There is also thought to be the
SO, WHAT ARE THE
POTENTIAL HARMFUL
EFFECTS OF HEAT STRESS
IN BIRDS?
● A decrease in egg size when temperatures exceed 24°C and, in
extreme cases, the cessation of egg
laying altogether
● Dehydration, which if severe
enough can kill birds
● Prolonged heat can induce a
moult in birds
● A decrease in the function of the
immune system
● Prolonged and excessive sunlight can lead to a reduction in the
colour of egg shells
● Temperatures above 43°C can
lead to death by hyperthermia
● Reduced feed intake leading to
poor production.
WHAT CAN BE DONE TO
IMPROVE THE SITUATION?
All strategies are designed to lower
the ambient temperature or
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POULTRY HEALTH
increase the ability of the bird to
lose heat.
This, in practice, involves
increasing the ventilation and
openings to allow fresh air to flow
in and pull out warm air. This will
also help to increase the air speed
across each bird.
Higher air speeds ensure adequate removal of the hot air
boundary surrounding each bird,
aiding convectional heat loss. This
is particularly important when
birds are close to peak stocking
densities.
“While
temperatures
above 27°C or
relative humidity
above 50% are
enough to cause
panting, the
negative effects
of heat stress
can be seen at
temperatures
above 24°C”
Increased flow also removes
humid air, a by-product of breathing. Reducing humidity allows
panting to be more efficient.
Recommended air speed in hot
weather is between 1.5 and 3
metres per second. This will need
to be measured at bird level and, in
practice, to achieve 3m per second
will be difficult in all but the more
modern sheds.
Looking at long-term investment, there are now renewable
systems that can be used in both
cooling and heating modes and
will both cool the air and the
‘under-floor’ heating pipes, allowing complete environmental con-
trol whatever the weather. Try to
provide shade for your birds if
they are a free-ranging flock,
although with certain farms established trees will already be doing
this job.
Encourage birds to drink and
provide electrolytes in the drinking water. The electrolytes are
designed to rebalance the potassium and carbonate level to reduce
the alkalosis. Electrolytes are more
efficient at hydration than plain
water alone and will help to reduce
mortality due to dehydration.
If birds are panting and stressed
then avoid stimulating the birds.
This may even involve avoiding a
shed walk in the heat of the day or,
in some situations, changing the
feeding patterns.
But this can cause problems due
to rushing for the food when reintroduced, so it should only be carried out under consultation with a
vet and feed adviser.
Reducing stocking density can
also greatly reduce the heat produced in a house. This is particularly true for broiler farms. However, catching and transporting
birds on a severely hot day can
cause even more problems with
heat stress and higher mortality
levels in those birds being moved.
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