Mountain of evidence

Credibility of coccidiosis vaccination becoming 'undeniable'

The use of coccidiosis vaccines has soared in recent years as progressive poultry producers seek ways to rejuvenate worn-out anticoccidials and find drug-free disease control methods.

Now, research is validating the trend.

At the last meeting of the American Association of Avian Pathologists (AAAP) in Denver, researchers presented a mountain of evidence supporting coccidiosis vaccination.

Of particular note was a talk demonstrating the ability of a live oocyst vaccine, Coccivac-B, to restore the effectiveness of a chemical anticoccidial in a broiler trial.

Major integrator's trial

The trial, conducted with a major US integrator, involved seven poultry complexes. A wide variety of in-feed anticoccidial rotation programs had been used. For one or two cycles the previous year, all programs had included the widely used chemical anticoccidial Clinacox (diclazuril).

First, litter samples were collected to obtain baseline diclazuril sensitivity information, said presenter Dr. Greg Mathis of Southern Poultry Research, Athens, Georgia, a key investigator in the study.

After collecting initial litter samples, four of the seven complexes continued their annual rotation using ionophores or chemical-ionophore shuttle programs for two cycles. The remaining three complexes incorporated two cycles of the vaccine into the annual rotation. The houses were then resampled.

Mathis determined diclazuril sensitivity by assessing weight reduction and coccidial lesion scores in test birds and comparing them to unchallenged controls. He then summarized diclazuril's efficacy as "good," "moderate" or "poor."

Vaccination improves sensitivity

In complexes that used ionophores or chemical anticoccidials, diclazuril sensitivity did not improve or improved little. But in the complexes that used two cycles of the vaccine in the rotation, diclazuril sensitivity improved significantly, Mathis said.

In fact, not one of the samples from houses that had used the vaccine tested "poor" for sensitivity in the study.

Further examination of the data showed that in one complex before vaccination, diclazuril sensitivity was rated "good" in only 30% of samples, but after vaccination, 100% of samples were rated "good."

In one complex where the vaccine had not been used, 25% of samples were rated as "good" for diclazuril sensitivity at the beginning of the study, but after continuing on a traditional rotation program instead of using the vaccine, 0% of the samples were rated "good," even though diclazuril had been "rested."

Results bolster early research

During his presentation, Mathis showed how the results of the trial bolster earlier investigations. As far back as 1976, a researcher showed that introducing massive numbers of drug-sensitive coccidia could replace drug-resistant coccidia.

In 1989, Mathis and associates found that they could improve the sensitivity of Amprol (amprolium) from 50% to 95% by using coccidiosis vaccination, which in this case was Coccivac-T for turkeys.

In 1994, noted coccidiosis researcher Dr. David Chapman of the University of Arkansas demonstrated that a field population of Eimeria was more sensitive to monensin after Coccivac-B was used. Then in 2000, another noted coccidiosis researcher, Dr. Harry Danforth of the USDA, showed that Coccivac-B use increased sensitivity to salinomycin.

In an interview after the presentation, Dr. Charles Broussard, worldwide poultry technical services manager for Schering-Plough Animal Health and coauthor of the paper, said, "The earlier trials focused on the ability of Coccivac- B to restore sensitivity to ionophore anticoccidials. Based on pen trials, we thought the vaccine also would restore sensitivity to the chemical anticoccidial diclazuril, but it hadn't been proved in the real world. Now it has."

Fine-tuning vaccination

In other presentations at the AAAP, investigators provided information that will help fine-tune the use of coccidiosis vaccination.

Dr. Steve Fitz-Coy of Schering- Plough Animal Health presented evidence from an epidemiological study demonstrating "considerable similarities" in the antigenicity of E. maxima field isolates. This study bolsters evidence that Coccivac-B provides a very high level of protection to most of the wild strains in the field today. In other words, poultry producers can rest assured that the immunity provided from Coccivac-B vaccination will provide protection against coccidiosis.

Dr. Steve Davis of the Colorado Research Center presented results demonstrating that 3-Nitro (roxarsone) has no negative effect on the immune status of birds vaccinated with Coccivac-B. Poultry producers can continue to use 3-Nitro in their program when they rotate to Coccivac-B.

Broussard said, "The credibility of coccidiosis vaccination is becoming undeniable.

"We can replace the amount of Eimeria resistance that's out there simply by incorporating Coccivac into the program and by making it part of a long-term control strategy. Introducing drug-sensitive coccidia into the house to replace coccidia that have lost sensitivity works."

Research confirming the usefulness of Coccivac-B in the field coupled with more information about how to "finetune" use of the vaccine will go a long way toward fostering development of useful, long-term coccidiosis control programs, he said.

"This is of huge benefit both to producers trying to restore the effectiveness of traditional anticoccidials and those who need to raise drug-free birds in response to market demand," Dr. Broussard said.

Source: CocciForum Issue No.8, Schering-Plough Animal Health.

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