would result in an economic loss of $7,000
per week or $350,000 per year.
Total losses to the U.S. industry, taking
into account differences in DPM susceptibility due to age, are projected at about
$16 million annually.
How and why DPM develops
DPM develops during repeated contraction of the muscles, when circulation
to muscle tissue is markedly increased
to supply oxygen and nutrients. The
muscles swell due to an increase in intracellular fluid. The tenders of chickens
increase in weight by about 20% due to
this swelling.
Most muscles have room to expand
so an increase in size does not impair
function. However, because broiler tenders lie in rigid compartments, bordered
by the sternum, keel and an inelastic
fascia, they cannot expand during activity. Therefore, muscle swelling impairs
blood flow due to an increase in intramuscular pressure (it “strangulates”
itself) and ischemia rapidly develops.
Why is DPM more prevalent?
It has been hypothesized that intensive selection for breast meat yield
once may have contributed to the
prevalence of DPM in turkeys, where
the defect appears to be inherited. Up
until 1990, few broilers were deboned,
and most were marketed whole or as
bone-in parts. Therefore, DPM typically went largely undetected at the
processing plant. The relatively few
lesions occurring were sometimes
discovered by consumers after cooking, which caused some complaints
and product rejects or returns. This
generally resulted in relatively minor
economic losses or hard-to-detect
losses in consumer acceptance.
Since the percentage of broilers that
are deboned, and hence the weights to
which they are being grown, have in-
creased steadily over the last 20 years,
both the incidence and detection of DPM
in the plant has increased. Concurrently,
there has been an increase in genetic
selection pressure for greater breast meat
yield in broiler stocks.
Broiler growth and yield studies
Over the last decade, research at
Auburn University has monitored the
occurrence of DPM through broiler
growth and yield studies with commercial strains of broilers. In these studies,
spontaneously occurring DPM varied
from 3% to 17%, seemed to be higher
in broilers with greater growth rates,
decreased in warmer weather, and was
more common in males than females.
More recently, an “encouraged wing
flapping” technique used to assess susceptibility to DPM has shown different
results. The gender effect was found to
be relatively slight, and the influence
of weight, when age and sex effects
were accounted for, was negligible.
However, DPM occurrence was greater
in breast meat yield than cut-up strains
of broilers.
DPM in broiler trials
In a limited preliminary trial on
likely causes of DPM in the industry, le-
sions spontaneously occurred in 12% of
control broilers, while only 5% of those
driven over migration pipes twice daily
from 10 to five days before slaughter
developed DPM. However, 20% of those
subjected to light intensity increases
and caretaker disturbances daily dur-
ing the same period developed DPM. In
research funded by U.S. Poultry & Egg
Association, the effects of concurrent
increases in light intensity and caretaker
disturbance in growing broilers is being
investigated.
Influence of activity, lighting
Differences in photoperiod and intensity are known to markedly influence
broiler activity. Increased activity levels
were hypothesized to reduce the occurrence of DPM development by keeping
tender muscles in better condition so that
they withstand periods of flapping that
might otherwise induce DPM.
Recently, the authors saw a reduction
in spontaneously occurring DPM when
broilers were provided ramps that had to
be climbed over and “flown” off of to go
from feed to water. However, activity inducing lighting programs had no effect,
and the incidence of induced DPM was
not affected by either ramps or shorter
photoperiods of brighter intensity.
These results indicate that while
ramps limited DPM susceptibility to
naturally occurring inducers, a lighting
program believed to increase activity did
not, and neither reduced susceptibility
to a strong artificial DPM inducer (the
EWF technique).
Controlling DPM
Multiple genetic, physiological and
management factors may play a role
in the DPM susceptibility of broilers.
At present, the key to controlling this
problem is to limit sudden and excessive
wing activity through reducing stress
and flock flightiness, particularly after
35 days of age.
Flightiness or excessive wing flapping may result from feed and water
outages, human activity in the house,
the use of loud equipment in or close
to the house, increased day-lengths or
light intensity, increasing light intensity episodically for flock inspection,
or house preparation for feed and water
withdrawal or catching. ■
