The Rural Voice, 2005-12, Page 35c
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"The reason we didn't lose too many
birds is that it was a dry summer,"
Huffman said. "We didn't have the
losses we could have."
Chickens are well insulated by
feathers that make it harder to lose
body heat. "I suggest to you that at
the typical density (of stocking birds)
that these birds are under stress
before a 40 humidex reading,"
Huffman said. "I think its about 38.
If you look at 38 (Humidex reading),
we're at 20 -plus days when birds are
starting to be heat stressed."
Using this barrier, the number
of hot, humid days jumped to
24 in Hamilton, 19 in
Waterloo and 21 in London.
(Huffman suggested poultry
producers considering a new location
might want to consider Mount Forest
which registered only 11 days with
over 30 degree temperatures and only
six days over 38 humidex.)
But humidity plays a
disproportionate role in raising the
humidex, Huffman explained. If the
humidity is greater than 50 per cent,
a figure often surpassed in a
traditional southwestern Ontario
summer, the dangerous level of heat
stress kicks in at a much lower
temperature. "We don't even need to
have 30 degree weather if the
humidity is high," he said. If
humidity is low, heat stress doesn't
kick in until a much higher
temperature.
High humidity wasn't a factor in
2005, Huffman said, but who knows
what the conditions might be in the
summer of 2006?
Dr. Babak Sanei, OMAFRA's
lead veterinarian for disease
prevention in poultry presented a
study based on the results of a 2003
study on heat stress that resulted
from the problems from the 2002
heat wave. The survey followed up
on a quick, one-page survey that had
been conducted following the 2002
crisis. A graduate student was
involved in working with 63 farms,
including 260 barns, to look at heat
stress problems. Several of the farms
had kept daily mortality records but
many more didn't, meaning the only
way to calculate mortality rates was
to look at mortalities for the whole
quota period. The farms were divided
into those that had a history of
greater than normal mortalities from
heat stress and those which didn't.
The farms classified as having a
history of heat stress problems
ranged from a six per cent elevation
in mortality to an extreme of 75 per
cent.
In order to try to isolate factors
that might affect heat stress losses,
the survey included building
specifics such as the floor area and
the size of building; ventilation and
cooling systems and management
strategies such as density, nutrition
and feed withdrawal.
Not unexpectedly, the size and
age of the birds was a big factor in
heat stress mortality. The comfort
zone is much different for older birds
than younger ones, Sanei said.
Chicks need to be at a warm
temperature during brooding but the
temperature is dropped as birds grow.
The greatest losses were among
flocks of birds 38 days and later and
2-2.5 kg. in weight.
The stocking density was a factor
in some individual flocks but was not
significant statistically across the
whole survey sample. One extreme
case of 16 per cent losses resulted
when barn renovations had seen bird
density increase to 2.7 kg per square
foot from the normal 2.4 ratio.
The most significant factor in the
difference between farms that had
problems with heat stress and those
that didn't was ventilation. In all
cases the barns without problems had
better ventilation systems.
The survey also looked at the
effect of perforated soffit in helping
to release buildup of heat in the attic
of barns and found 67 per cent of
those barns with no problems had
this improved airflow versus 48 per
cent of those barns with heat stress
problems.
By the summer of 2003, 15 per
cent of the producers who had
suffered losses in 2002 had installed
cooling systems to help prevent a
recurrence. The most affected farms
also adopted new nutrition regimes
and management strategies.
One of the most common
strategies among farmers is
withdrawal of feed from chickens.
But Sanei pointed out it's important
that all feed should be withdrawn and
that it's done early enough in the day.
The theory is that the bird produces
the most heat as it metabolizes its
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