"Once the birds had been on the vaccine for 35 days, we had no more dermatitis."
DR. STEVE RONEY

Researchers are making significant strides in understanding the mechanisms behind gangrenous dermatitis in poultry. But while researchers continue experimenting in their labs and making observations at posting sessions, broiler growers are learning about GD, too—practical and sometimes tough lessons from their day-to-day operations.

At the Intestinal Health meeting in Orlando, Dr. Steve Roney, formerly director of veterinary services, eastern region, Gold Kist, Inc., and now a US-based veterinary consultant, said he has faced challenges with gangrenous dermatitis on nearly a daily basis for much of the past 7 or 8 years. "It's one of the most complicated syndromes I've ever dealt with."

Experience with larger birds

Roney first discussed some experiences he had with a complex that grew primarily large birds. The operation was having problems with GD and Roney was writing two or three penicillin prescriptions weekly.

"This is a complex that was moving 1.8 million birds a week," he added. "We were losing overall a 0.25% livability due to gangrenous dermatitis. That's 4,500 chickens per week. So that disease alone—without any of the other costs of growing the chicken—was costing us $10,000 each week."

The birds had been on a nicarbazinionophore shuttle program before Roney decided to switch to Coccivac-B in the early spring.

"Our last case of dermatitis was in one of the birds that was on the nicarbazinionophore program," he said. "Once the birds had been on the vaccine for 35 days, we had no more dermatitis."

Roney reminded the audience that the move to coccidiosis vaccine was made in April, just as the environmental challenge from weather was easing. "So, would it have stopped anyway? I don't know. But we've seen over and over that these things happen when we move to the coccidiosis vaccine."

The veterinarian said one explanation could be that in shifting coccidia cycling to earlier in the bird's life, there is less stress on the bird later, making it less vulnerable to GD.

Antibiotics posed challenges

At one plant that produced three different sized birds, the use of antibiotics posed challenges. "We have run vaccine on the birds that are 3.90 lbs. in weight. We find that if we don't fortify the diet early with protein we lose about 3 points in feed conversion," which he thinks is a viable approach if ionophores are losing efficacy.

Generally, however, the company is steering away from 3.90-pound (1.77 kg) birds until more is learned about how to fortify their diets and maintain feed conversion when changes are made in their program. "But anything over 4.40 pounds (2 kg) is fair game right now," Roney added.

Under the present strategy, the complex utilizes a coccidiosis vaccine every year for two to three cycles; the program varies depending on the size of bird. He said the approach has worked well. "It's helped us keep our ionophores in much better shape than they would have been, in my opinion."

Another complex operated by the company had been utilizing a rotation program of ionophores for years, but Roney said that within the first cycle the houses would break with Eimeria tenella and with E. maxima. That operation produced a colored bird, and he said he and his team had initially been very reluctant to add coccidiosis vaccine to the program, thinking it might cause a loss of color in the birds.

"But it got to the point where we had no choice," he said. "A lot of things you do it's because you have no choice."

Coccivac-B was added to the program. In addition, they decided to include a three quarter dose of roxarsone, the arsenic derivative anticoccidial, but only in the grower ration. Their reasoning was that the drug wouldn't be needed in any other ration because it was summer and the birds they were dealing with were large.

The results?

Gangrenous Dermititis

Though GD manifests primarily on the skin, many researchers are convinced intestinal factors play a role in its etiology.

"Lo and behold, we lost no color—we never had a complaint about that," Roney said. "And the birds had some of the best performance they've ever had."

Roney said the complex is now using coccidiosis vaccine on a yearly basis.

Testing the coccidia-cycling theory

Roney and his colleagues then wondered what factors were causing these decreases in the incidence of gangrenous dermatitis.

Was it an indirect benefit of using the coccidiosis vaccine? Did vaccination shift the cycling of oocysts back a few days, therefore taking away the 30-day challenge from the birds? And, if that were so, might the same results be obtained using an in-feed anticoccidial instead of the vaccine to thwart that late coccidiosis challenge?

To find out, Roney decided to take a different approach. Instead of using the vaccine to shift the coccidiosis cycle, he instead added the anticoccidial Clinacox (diclazuril). "We put it in for 7 days in the first withdrawal," he added. "Based on the posting sessions we'd had, that seemed to be where we were getting the heaviest challenge from E. maxima."

When the birds reached about 35 days, problems with gangrenous dermatitis subsided. Roney emphasized, however, that other factors might have played a role in the decrease of GD.

"We had made a minor change in the feed—removed some bakery byproduct," he said. It is difficult to know for certain whether the byproduct was contributing to the problem, he added, because another broiler complex—one that did not have problems with dermatitis—was also using the bakery product. He thinks the reduction in incidence of GD could have been due to a combination of factors.

Spring 2008

Regresar a North American Edition (#1)