Monitoring coccidiosis patterns can improve bird performance, profits
Producers looking for ways to improve
bird performance and their bottom lines
were advised to put more emphasis on
routine monitoring of coccidial patterns
in their flocks.
“Sometimes what’s not seen can hurt,”
said parasitologist Dr. Steve Fitz-Coy.
Without monitoring, coccidiosis could be
taking a serious but unrecognized toll.
As it is now, many poultry producers put
coccidiosis control on the back burner —
until it becomes a problem. In the
meantime, performance may suffer and
dollars are lost, said Fitz-Coy, of Intervet/
Schering-Plough Animal Health.
In addition to monitoring coccidiosis
patterns, he encouraged producers to
avoid choosing the least expensive
coccidiosis-control program. It’s understandable,
considering the rising costs
of production, but what might initially
seem less costly may not be the most
cost-effective over the long-term.
Coccidiosis, Fitz-Coy emphasized, is a
dynamic disease and the patterns may
change. That’s why monitoring is
important. It can reveal trends within a poultry operation that tell producers
whether a coccidiosis-control program is
working or that it needs to be modified.
Coccidia, which are present in virtually
all commercial poultry houses, can cause
tremendous destruction of bird tissues,
which leads to impaired food intake,
digestion and absorption. The result is
weight loss, poor feed utilization, poor
pigmentation and even mortality, he said.
Many poultry producers put
coccidiosis on the back
burner...
performance may
suffer and dollars are lost.
The damage caused by coccidial organisms
is directly related to the number and
species of
Eimeria ingested, he said.
Controlling coccidiosis requires maintaining
a low parasite burden, which is
accomplished by keeping the coccidial
intake and replication rate low, which in
turn results in minimal cell destruction
and less impact on bird performance,
Fitz-Coy said.
Complicating the issue is the development
of drug tolerance or drug resistance to the
in-feed anticoccidials that producers have
relied upon for so long, he continued.
“Rotation of drugs alone to combat drug
tolerance or resistance is futile,” Fitz-Coy said. Successful coccidiosis control may
require rotating multiple in-feed anticoccidials
in conjunction with live, effective
vaccines. He also recommends routine
necropsy sessions, regular testing for
drug responsiveness with anticoccidialsensitivity
testing (AST) and conducting
regular oocyst counts from litter or
droppings, he said.
Fitz-Coy noted that several monitoring
options are available and each has its own
positives and negatives. Using a combination
of methods consistently will provide
useful and reliable data.
He cited examples from three different
commercial poultry operations in different
regions of the US to underscore his point
that monitoring the pattern of coccidia
and coccidiosis change is crucial.
In one complex, for example, necropsy
data over several years showed that
the prevalence of
Eimeria acervulina,
E. maxima and
E. tenella was 33%,
45% and 9%, respectively.
During the early years,
E. acervulina
was more prevalent than
E. maxima
(see Figure 1). But with the use of
certain anticoccidials during summer
months, the prevalence of
E. maxima
increased and remained fairly high.
Figure 1. Necropsy data show that in early years,
E. acervulina was more prevalent than
E. maxima,
which increased and remained high with the use of a specific anticoccidial.
In the winter months, the prevalence
of E. acervulina trended downward and
appeared to be associated with the use of
a specific in-feed anticoccidial. The AST
data were in agreement with the findings
from necropsy data, leading to changes in
the coccidiosis program and improved
coccidiosis control.
Which species is it?
Identifying which coccidial species is
affecting flocks is an important part of the
coccidial-monitoring process, Fitz-Coy emphasized in a second presentation at
WPDC. He compared coccidia to zebras,
which appear the same at first glance,
even though each species is significantly
different from the other.
“It’s the same with coccidia. Each species
is unique, has unique pathology and
pathogenicity and even drug responsiveness,”
he said. Each species also must
be treated as unique to achieve good
coccidiosis control.
Features that differ among various
Eimeria include fecundity — the ability
to produce oocysts (eggs) — the region
of intestine that each species parasitizes
and the depth of parasitic development
in the mucosa. Different species of
Eimeria also vary in the size of their
coccidial-endogenous (developmental)
stage. The pathogenicity is influenced
by these various characteristics,
Fitz-Coy explained.
Eimeria praecox has relatively high
fecundity but is a shallow invader of the
mucosa and produces relatively small
endogenous stages, he continued.
E. tenella has moderately high fecundity,
is a deep invader of the mucosa and
the endogenous stages are large.
E. necatrix is a poor oocyst producer but
is a deep invader with relatively large
endogenous stages.
Because of these traits, E. praecox is
considered non-pathogenic, while
E. tenella and E. necatrix are highly
pathogenic to chickens, Fitz-Coy said.
E. brunetti, E. maxima and E. mivati
also develop deep into the tissues.
Mature stages damage blood vessels,
which results in bleeding into the
intestinal lumen, he said.
Coccidial species that have a longer
pre-patent period tend to be more
pathogenic than those with shorter
periods. The pre-patent time is how
long it takes for the first appearance
of oocysts in the feces of chickens after
they are infected with Eimeria, and this
pre-patent time can be used to help differentiate various species of Eimeria,
he said. E. praecox has the shortest
pre-patent period — 84 hours —
compared to 138 hours for E. necatrix.
Another way to differentiate Eimeria
species is by their size and shape when
viewed under a microscope, although it
can be challenging and requires someone
skilled at the art of oocyst identification.
The oocysts of E. mitis, for instance,
are almost round, and the oocysts of
E. maxima are large and have a tint of
color. The size and shape of the nonpathogenic
E. praecox can be hard to tell
apart from E. tenella, E. necatrix and
even E. brunetti.
Advanced procedures such as polymerase
chain reaction (PCR) can be useful but
may not be able to identify all Eimeria
species, Fitz-Coy said.
“The best approach for differentiating
various species of coccidia may be using
multiple methods of identification, such
as parasite biology as well as PCR,”
he said.
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