April 2013 - AFMA

ing heat stress, would be helpful. Minerals
can be provided from high bio-available
sources like complex trace minerals, Zn,
Cu, Mn and Cr. This would also help to reinforce
the immune system and reduce infectious
problems (Tomlinson et al., 2008). By
providing sodium bicarbonate to replenish
the carbonates lost in the urine would also
prevent metabolic acidosis.
It is desirable that animals have the
benefit of being exposed to lower temperatures
during night time. Despite high
ambient temperatures during the day, a
cool period of less than 21⁰C for three to
six hours will minimise the decline in milk
yield (Igono et al., 1992).
Poultry
When chickens are exposed to hot weather,
they seek comfort in the house, stop eating
and pant. Birds do not have sweat glands
like mammals and the body is covered by
a thick feather cover. They display ruffled
feathers when kept under these conditions
(Daghir, 1998; Reece et al., 1972). Panting
starts off by being fast and superficial, but
if exposure is prolonged it becomes deep
and slower and then respiratory alkalosis is
developed. Capillary beds are dilated.
The immune response is compromised
during heat stress (Gross & Siegel, 1983; Lin
et al., 2005; Tirawattanawanich et al., 2011),
so care must be taken to avoid exposure
to infectious agents. Mortality can happen
within minutes once birds have reached
this point of alkalosis and hundreds or
thousands of birds can die. Performance
losses in these birds reaching market age
include poor performance and losses in
processing plant yield (Ryder et al., 2004;
Renaudeau et al., 2011).
The following approach classifies the
actions to be taken considering the target
objectives pursued to minimise losses during
heat stress:
Reducing body heat production
Reducing stocking density is strongly
recommended in hot climates – below
35kg/m 2 in cases of tunnel ventilated
houses and below 12 birds/m 2 (25kg/m 2 )
in open-sided houses. During the brooding
phase, try to give birds full access to
the space of the house.
Proteins in the diet cause the highest
heat increment, so accurate amounts are
recommended according to feed consumption,
providing a good amino acid
balance (Daghir, 1998; Lu et al., 2007).
Feed restriction is probably the most
used practice in broilers to avoid mortality
(Daghir, 1998; Zulkifli et al., 2000). It is
mostly used in non- or incomplete technified
operations. Tunnel ventilated houses
do not use it unless facing an unusual
situation. It is recommended mostly during
the beginning of the hot season when
birds are being exposed to heat during the
first few weeks. Feed access is removed
for six hours during the peak hot time and
then two hours of light during the night
are given to compensate. Midnight feeding
is also practiced with broilers, especially
in open-sided houses (Daghir, 1998;
Renaudeau et al., 2011).
Increasing airflow
New production systems consider the use
of tunnel-ventilated houses with negative
pressure provided by a set of fans
(132cm) on one extreme of the building
that pull the hot stale air out. The air enters
the building on the other extreme of the
building through a filter that can be wet
or dry, depending on the need of the micro-environment
inside the house (Lacy &
Czarick, 1992). Approximately 152 to 244m
per minute is commonly used in these kinds
of houses (Lacy & Czarick, 1992). These systems
imply good sealing, quality of materials
and construction, as well as high-energy
use (dependable power supply).
Open-sided houses are still being used
in tropical countries and in some cases performance
is efficient enough to keep in production.
These systems exploit the adaption
process of the chicken. However, in the case
of a heat wave that exceeds the adaption
limit, big mortalities may occur. In this case
the money saved by cheaper facilities and
lower energy consumption is exceeded by
the losses. Many layer farms have these systems
with some comfort provided by some
fans and sprinklers/foggers.
Evaporative heat loss
The use of wet panels in the inlets of poultry
houses is a common practice. The comfort
sensation when humidity is incorporated
increases substantially. The use of foggers
is also very common at the peak time of
hot weather condition. In dry hot weather,
this evaporative cooling is essential and accounts
for the main heat loss mechanism.
Soaking of birds is not a common practice,
but it is still done in some hot weather
producing areas. It is done manually as an
emergency measure and it has shown good
results.
Compensating for negative effects
Full water access must be provided as birds
increase water consumption during hot
weather. A major problem in poultry production
is the reduction in feed intake, but
also the reduced efficiency derived from
the compensation process in the body.
As mentioned, from a nutritional standpoint
some changes in the diet have proved
to provide great value: Increase in nutrient
density, replace as much energy as possible
by fat sources, improve amino acid balance,
increase vitamins E, C and A, as well as trace
mineral fortification. Do not increase protein
– just provide a good amino-acid balance,
as an increase in protein has proved
to increase fat deposits in the carcass.
The use of electrolytes in water also
helps to replace the main ions lost. Solutions
of NaCl and KCl can be added when
heat waves are hitting.
Acclimation to high ambient temperatures
happens to animals chronically exposed
to hot weather conditions (Yalçin
et al., 2000; Yahav & McMurty, 2001; Yahav,
2009). It consists of anatomical and physiological
changes developed by the body
of the animal to reduce heat production
and increase heat loss, preventing a longer-term
exposure. Studies need to be done
to learn to what extent the animals can be
tested, the type of acclimation processes
and the nutritional plane they would require.
Given the physiological adaption processes,
profitable and competitive performance
still needs to be obtained. Providing
maximum comfort can become extremely
costly to achieve. However, taking advantage
of some adaption process could help
to make production feasible in tropical and
subtropical countries.
References are available from AFMA on
request.
Processing
AFMA MATRIX ● APRIL 2013 21