Postcard: Barcelona
Necrotic enteritis (NE) research is demonstrating that the disease is highly age-specific and that the pathogenicity varies widely depending on the strain of Clostridium perfringens (CP) causing the disease, said Steve Davis, DVM, president and CEO of Colorado Quality Research, Inc., Wellington, Colorado, USA.
A severe NE challenge is most likely to occur between 14 to 24 days of age and even more so at 17 to 22 days of age, he said.
Some CP isolates are pathogenic without any apparent primary trigger, others require one or more triggers and “some we still can’t recreate with isolates from field outbreaks,” Davis said. The variations in CP isolates may explain why some production complexes have severe NE problems without any management causes to explain them, why others have no NE and why some NE-control programs work in one complex but not another.
The characteristics of NE outbreaks vary widely too, he said. Some create acute disease and mortality within hours of oral challenge, but others are slower in onset and last longer.
Risk factors
Risk factors for NE include certain types of nutrition and management factors, Davis continued.
“The gut is a culture tube,” he said, and any change in diet or increase in feed consumption can cause intestinal irritation, raising the risk for NE and its severity. High levels of animal byproducts, for instance, have been linked to NE. Furthermore, animal byproducts contaminated with CP spores are a likely source of pathogenic CP. Feeding an all-vegetable diet to vulnerable flocks may help control the disease.
Davis cited a host of management factors that may contribute to NE, including new, clean litter, which decreases the development of immunity. Feed outages, overeating, a coccidiosis challenge, chilling, high bird density and fast-growing bird breeds are also linked to the development of NE. “Slow-growing birds are much less likely to develop NE,” he noted.
Even lighting programs with long light cycles have been linked to an increased risk for an NE outbreak, indicating it may be beneficial to restrict the length of light cycles in flocks breaking with NE; shorter light cycles slow bird feed intake and growth, thus decreasing the incidence and severity of NE, Davis said.
Traditionally, NE has been managed with antibiotics added to the feed or water, but Davis said vaccination could prove to be a valuable tool in many production systems. Progeny of broiler breeders vaccinated with Netvax, a CP toxoid, provided the best reductions in the incidence and severity of NE and mortality from the disease when the challenge was at 14 to 15 days or at 21 to 22 days of age; the most impressive results were obtained when the challenge was highest, he said. In addition, passive immunity lasted through the specific age-range risk for NE in broilers.
“The earlier in life that CP immunity is developed, the better,” Davis said.
NE vaccine shows promise in Europe, too
Netvax, a Clostridium perfringens toxoid for reducing mortality and the incidence and severity of necrotic enteritis (NE), may be one of several tools that can help reduce the use of antibiotics in broilers, said Matthias Hausleitner, DVM, a consulting veterinarian in Germany.
In controlled field trials with Netvax conducted from October 2010 to June 2011, no adverse effects were seen in broiler chicks from vaccinated hens, and no NE occurred. Performance of the chickens and slaughterhouse data were good and there was a low use of antibiotics, he said.
Flock management was found to have a major influence on outcome in vaccinated birds; farms with average management standards had better average weight gain, a better feedconversion ratio and had to use fewer antibiotics against Gram-positive bacteria than farms with lower management standards, Hausleitner said.
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