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Birds vaccinated for coccidiosis may face enteritis threat, but losses are easy to avoid with good management and common sense

Cherry: Live oocysts enable them to develop immunity.

Many poultry producers believe that chickens vaccinated for coccidiosis are more susceptible to necrotic enteritis than those receiving in-feed coccidiostats.

According to Dr. Tim Cherry, poultry veterinarian at Stephen F. Austin State University, Nacogdoches, Tex., this belief comes from the fact that birds vaccinated for coccidiosis receive live oocysts that enable them to develop immunity against coccidia organisms.

"For the vaccine to work, coccidial organisms have to invade the intestinal tract and reproduce, which stresses the gut," he explains. "This irritation in the gut can provide the environment necessary for Clostridium perfringens - already present in the gut "to produce toxins that cause necrotic enteritis."

But that doesn't mean necrotic enteritis can't be managed in birds vaccinated for coccidiosis.

As Dr. Larry McDougald, professor of poultry science and a parasitologist at the University of Georgia, Athens, puts it: "The vaccine isn't introducing anything new into the matrix."

Tapping Natural Resistance

Most birds are exposed to coccidia whether they receive the vaccine or not, so they're naturally vulnerable to C. perfringens infection. In the end, poultry specialists say, it all comes down to good management and common sense for keeping necrotic enteritis in check "regardless of whether birds are vaccinated or medicated for coccidiosis.

While it's true that coccidia - whether acquired naturally or through vaccination "introduce live parasitic organisms into the intestinal tract of birds, birds exposed to oocysts by vaccination get a controlled dose of known type, says Dr. Linnea Newman, a consulting poultry veterinarian based in North River, N.Y.

By following proven management techniques and providing proper bird space, adequate ventilation and reduced litter picking, producers can help the parasites cycle through the healthy bird's system while tapping its own natural defenses to reduce the threat of necrotic enteritis, she adds.

"We see a minimum of lesions with Coccivac-B when birds are handled well and the full level of bacitracin, virginiamycin and lincomycin is used through at least day 17," stresses Newman.

"But don't use antibiotics as a crutch," she warns. "Necrotic enteritis control has to start with good management and sanitation, which will become even more important as the poultry industry backs off or eliminates in-feed medications in response to growing consumer demand for natural birds."

Stay on Track

Factors ranging from grain type and wet litter to vaccinations and ventilation can also play a role in increasing irritation in the gut, which in turn promotes the growth of toxins resulting in necrotic enteritis.

Follow this checklist to make sure your control program is on the right track:

Irritation in the gut can help C. perfringens produce toxins that cause necrotic enteritis.

"� Fine tune diets. Cut back or eliminate wheat, at least in the starter ration. Wheat has been associated with an increased incidence of necrotic enteritis, says Cherry."The use of an antibiotic or growth promotant helps hold down intestinal irritation," adds Dr. Rex Bushong, Texan Six Consulting Firm, San Angelo, Tex. The full complement of vitamins, minerals and trace minerals should be part of the ration as well.

"� Lower bird density. "We're at about .75 square foot per bird or 15 birds per square meter," says Dr. Harry Danforth of the USDA. "One square foot per bird or 11 birds per square meter would help control necrotic enteritis and may be necessary to control necrotic enteritis under antibiotic-free conditions."

"� Provide a cleaner environment. C. perfringens is spread through feces, so good sanitation is important. "Physical cleaning is the cheapest method of breaking the cycle of clostridial diseases," Drs. R.A. Nortonand F.J. Hoerr of Auburn University wrote in a recent article.¹

If a flock has experienced diseases such as necrotic enteritis, "the litter should automatically be cleaned out completely before any new flock is brought onto the premises," they report.

"� Check the litter. Field observations indicate that high litter moisture encourages necrotic enteritis, according to Newman. Use an absorbent litter material such as wood shavings or rice hulls and maintain litter depth of at least 3 inches. "The best way to control litter moisture is to ventilate, ventilate, ventilate," she adds.

If the litter is found to be alkaline, which can result from applying lime, it should be treated to adjust the pH Cherry adds, "Changing the top of the litter with litter acidifiers makes the environment less suitable for bacterial growth."
"� Control access to bacteria. According to Newman, infection occurs when bacterial numbers overwhelm the flock's ability to resist infection. One of the biggest factors in bacterial access is litter picking.

"Growers should closely monitor feed availability to avoid litter picking," says Newman. "Frequent disinfection of water systems is also important."

"� Watch down time. "Producers using intense management, including crowding birds and short down times of less than 12 days between flocks, are asking for trouble whether they're using an antibiotic or vaccination program," says Bushong. He recommends a minimum of 14 days down time.

1. Poultry Digest, August/September, 1999.

Source: CocciForum Issue No.4, Schering-Plough Animal Health.

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