Alfonso: 'We showed improvements in livability and feed conversion'
"We think growers
who protect their birds against clostridium may see other improvements too."
DR. MATILDE ALFONSO
Although some broiler producers are
backing off ionophore antibiotics for
controlling coccidiosis in broilers, a good
number still rely heavily on the use of
those agents—at least for now.
To find out how its new Clostridium
perfringens type A toxoid would control
necrotic enteritis (NE) in these types of
operations, Schering-Plough Animal Health
conducted a huge trial involving nearly 22
million broilers.
Dr. Matilde Alfonso, a technical services
veterinarian for the company who was
involved with the trial, explained that the
design of the study was straightforward—compare the progeny of vaccinated hens
with those of non-vaccinated hens.
Developing such a pure comparison in
real-world field conditions created some
challenges, however.
"Most growers stock their barns with birds
from different breeder sources, so that
made it tough to find a 100% vaccinated
flock," she explained.
That being the case, researchers decided
that flocks with 70% or more of birds vaccinated
would be evaluated as part of the
vaccinated group. Flocks with less than
70% vaccinated birds served as controls.
In all, more than 750,000 hens were
vaccinated. Vaccinated birds received a
0.5-ml subcutaneous injection of the NE
toxoid at 10 weeks of age and a booster at
18 weeks. Researchers then followed 22
million of their progeny, along with controls,
over a 6-month period.
All birds were fed a standard corn-soybean
mix, with an in-feed ionophore. "No antibiotic
growth promoters were used," Alfonso
said, "and that's a key point" of the study
because those compounds help to control
necrotic enteritis.
There was considerable variation in the
size of the birds included in the trial,
ranging from 4 to 6 pounds (1.81 to 2.72 kg).
There was variation, too, in the respective
locations of the four farms that took part in the study, with operations scattered across
a wide geographic and climatic range.
Figure 1. Trials showed an improvement in livability of 0.42% with significant reductions in feed conversion. Calorie conversion and adjusted calorie
conversion also improved, as did standard cost.
Moving on to results of the trial, Alfonso
emphasized that incidence of necrotic
enteritis on these farms was historically
low, seen in only 0.07% to 1.1% of flocks
each month.
"The anticoccidials were keeping the lid
on necrotic enteritis," she said. "The
incidence was very sporadic."
So how did the progeny of the NE-toxoid
vaccinated birds compare with progeny of
non-vaccinated birds?
"We saw positive trends for the NE
toxoid in each of the individual study
complexes," Alfonso reported, adding
that some trends for individual complexes, when evaluated individually, did not
reach statistical significance.
That changed, however, when the data for
the study sites were combined (Figure 1).
Alfonso said that by pooling the results and
thereby increasing the sample size, some of
the differences in the two groups became
statistically significant.
"We showed an improvement in livability of
0.42%. We also got a significant reduction
in feed conversion," she said of the progeny
from the vaccinated hens. "Both calorie
conversion and adjusted calorie conversion
improved, -13 and -15, respectively, as did
standard cost, which went down by 0.001
dollar per pound of live weight."
Average weight and rates of daily gain
also showed an increase, though those improvements were not statistically
significant. "But the trend was positive,
and that's what counts," she said.
Alfonso noted that overall, the progeny of
NE-toxoid vaccinated hens showed better
performance. "And we think that may be
due to the vaccine controlling subclinical
necrotic enteritis, which in turn may help
reduce other health problems that tend to
be associated with NE."
She added that she thinks growers who are
seeing poor performance in their flocks
might benefit from using the new NE toxoid.
"And we're not just talking about mortality
here," she emphasized. "We think growers
who protect their birds against clostridium
may see other improvements too."
Spring 2008
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