Two clinical field trials conducted in Europe demonstrated that vaccination of hens with Netvax, a Clostridium perfringens type A toxoid vaccine, prevented development of NE in broiler progeny, reported Dr. Luciano Gobbi, Intervet/Schering-Plough Animal Health’s technical manager for poultry, Italy.

Netvax, 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 Netvax 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 with Netvax 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 intramuscular 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 alphatoxin 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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