Necrotic enteritis outbreaks in broilers stop after vaccination of hens with clostridium toxoid

Outbreaks of necrotic enteritis in conventional broiler flocks stopped after breeder hens were vaccinated with a new clostridium toxoid vaccine, Dr. Neil Ambrose said at the European Poultry Conference held last fall in Verona, Italy.

The initial experience with the vaccine indicates that "passive immunity to Clostridium perfringens type A alpha toxin appears to be a viable strategy for the control of necrotic enteritis in broiler chickens," said Ambrose, director of veterinary services for Sunrise Farms of Surrey, British Columbia, Canada.

The vaccine, Clostridium perfringens type A toxoid, was developed by Schering-Plough Animal Health and is the first product of its kind for poultry, although clostridium toxoids have been used in other species for many years. Two doses of the vaccine are administered to hens, initiating immunity to the alpha toxin produced by C. perfringens, which is the most common cause of necrotic enteritis in chickens. The hens pass on the immunity to their broiler progeny.

Necrotic enteritis, Ambrose said, can be devastating, resulting in high mortality and reduced feed intake, weight gain and flock profitability. The problem is especially difficult to control in birds on wheat-based rations, which are common in Canada.

Poultry specialists throughout the world met in Verona, Italy, last fall for the XII European Poultry Conference.

With a trend in many parts of the world towards the production of broiler chicken meat without the aid of antibiotics, including ionophore anticoccidials, Ambrose started trials for Sunrise Farms by using a live coccidiosis vaccine instead of an in-feed anticoccidial in wheat-fed birds. However, in 2005, the company had six consecutive cycles of about 30,000 birds that experienced necrotic enteritis outbreaks. The birds had received Coccivac-B, a non-attenuated coccidiosis vaccine based on live Eimeria field strains, at day-of-age and the in-feed antibiotic- growth promoter bacitracin and/or virginiamycin.

Three of the flocks also received the anticoccidial salinomycin, which was added to stem the necrotic enteritis outbreak, but did not.

For each flock, there were two peaks in mortality attributed to necrotic enteritis, which occurred at about 19 and 27 days of age. Both roughly corresponded to expected peaks in coccidial cycling from the non-attenuated vaccine, he said.

"It is likely that the combination of intestinal viscosity associated with the wheat ration and the mucosal disruption caused by the normal cycling of the coccidial vaccine allowed the overgrowth of C. perfringens, triggering the necrotic enteritis events," he said. "There was no evidence of coccidial lesions outside of the normal expected levels for the coccidial vaccine, which appeared to be performing normally, with adequate development of immunity to coccidiosis."

Trial flocks

Sunrise Farms wanted to determine if passive immunity provided by the new clostridium vaccine could replace or augment in-feed antibacterial medication given to broilers that are fed a wheat-based diet, which is common in Canada, he said.

The company grew two broiler flocks from hens that had received the toxoid vaccine. Both flocks were vaccinated with Coccivac-B at day-of-age and the broilers, which totaled about 24,000 in number, received only the growth promoter bacitracin in the starter, grower and finisher rations. No in-feed anticoccidial was provided (Table 1).

The results with these test birds were compared to the six flocks that had experienced necrotic enteritis outbreaks and were from hens not vaccinated with the clostridium toxoid. All the birds had received the same wheat-based diet.

Among birds in the test group, "there was no evidence of necrotic enteritis in random birds, culls or mortality upon post-mortem examination, which also verified continued cycling of the coccidiosis vaccine at acceptable levels," Ambrose said.

Table 1. Medication regimens for flocks that did and did not experience necrotic enteritis outbreaks.

Better growth after toxoid

Growth performance in the flocks from clostridium-vaccinated hens met breed standards and, in fact, surpassed growth in the control group, explained Ambrose. These results were achieved in the second flock despite severe
heat stress at 27 days of age due to unseasonably high environmental temperatures, he said.

"Passive immunity against the C. perfringens type A alpha toxin appeared to successfully augment infeed medication to prevent lesions of necrotic enteritis when a non-attenuated coccidiosis vaccine was used in concert with a wheat-based ration," Ambrose concluded.

Sunrise Farms, he added, was planning further testing to determine whether passive immunity provided by the clostridium vaccine could control necrotic enteritis when reduced levels of in-feed medication are given or in the complete absence of in-feed medication.

Editor's note: For more information on the experiences of Sunrise Farms, see the article that begins on page 11.

Source: Cocciforum, isuue 13