NE vaccine trials in Europe
Two clinical field trials conducted in Europe demonstrated that vaccination
of hens with a Clostridium perfringens
type A toxoid, or necrotic enteritis (NE) vaccine, prevented development of NE
in broiler progeny, reported Dr. Luciano Gobbi, Intervet/Schering-Plough
Animal Health’s technical manager for poultry, Italy.
The vaccine, which contains a toxoid of
C. perfringens type A toxin, was administered to hens to convey immunity against NE to their progeny via passive transfer
of maternal antibodies.
Investigators conducted trials on commercial farms in Italy and Germany as part of the application process for licensure of the vaccine in the EU.
They used mortality, evidence of
C. perfringens type A-associated gut lesions, weight gain and feed-conversion ratio to evaluate vaccine performance.
The investigators also monitored antibody levels in vaccinated breeder hens, their eggs and in hatched, 7-day-old progeny.
Vaccinating breeders induced a significant antibody response against C. perfringens alpha-toxin, Gobbi said. This response was found not only in breeders but also
in their eggs and in serum from progeny chicks. The high antibody titers were reflected in the level of NE infection. None of the progeny of vaccinated
breeders had C. perfringens-associated
gut lesions, but control birds did.
Weight gain and feed-conversion ratios were satisfactory and within the standards of the two poultry companies hosting the trials. And with one exception caused
by a yolk-sac infection rather than NE,
mortality figures in the trials favored
the vaccinated birds’ progeny, compared
to controls.
Investigators also measured clinical
safety and reported no animal health
or welfare issues due to the vaccination
of breeders. Birds received intra-
muscular vaccination in the breast, although the toxoid vaccine can also
be given subcutaneously.
Gobbi noted that although clinical
NE can cause significant mortality,
the underlying costs of subclinical
disease — estimated at US $0.05 per
bird — should not be discounted.
In addition, 95% of NE that occurs
is subclinical.
Protection of broilers against the alpha-toxin through maternal antibodies lasted for about 3 weeks, Gobbi explained in
an interview with Intestinal Health.
By the time antibody titers dropped,
the birds’ gut development was
sufficiently advanced to establish their own immunity.
Gobbi, who was lead investigator for
the trial in Italy, said that poultry
companies involved in the trials are
interested in using the vaccine, once
registration is completed, probably
in 2009.
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