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Veterinarians, nutritionists and live-production managers flock to Missouri for the lowdown on new approaches to coccidiosis management in growing poults

It's no secret that coccidiosis is a potentially serious problem for the world poultry industry. But while the world turkey market may be smaller in numbers, the disease and, to some extent, current management programs, have even greater potential to shortchange producers on performance and profits

Here's why:

First, the cycle for growing turkeys is considerably longer than for other commercial fowl. So turkeys have a longer period of potential exposure to coccidiosis as well as other disease organisms. And any factor "whether it be disease or some other problem - that impedes a bird's uptake of nutrients is likely to have a negative impact on the bottom line

Fortunately, much progress has been made recently in controlling coccidiosis in turkeys. A recent Cocci- Forum conference of turkey producers held in Branson, Mo., "New Strategies for Coccidiosis Management," brought together representatives from growers representing 79 million birds, or onethird of the total US production.

Coccidiosis: Reviewing the basics

Dr. John Radu, a technical service veterinarian for Schering-Plough Animal Health, kicked off the conference with a review of coccidiosis-management basics. His presentation included a general overview of coccidiosis in turkeys and the protozoan parasite Eimeria that causes the disease.

Seven species of Eimeria are present in turkeys, he explained, but only four are pathogenic. Those are E. adenoides, E. gallapavonis, E. meleagrimitis and E. dispersa.

The main source of Eimeria infection is from birds actively shedding oocysts of Eimeria in their feces. Oocysts are essentially the developing eggs of the Eimeria coccidia. Infection in the flock spreads as other birds peck in the litter or consume feed or water that's been contaminated by the coccidia.

"It's extremely difficult to estimate the total impact of Eimeria infections," Radu told attendees. "That's because Eimeria tends to have very complex interactions with other organisms."

Radu also said a variety of other factors such as seasonal variations in temperature and humidity (litter moisture), are particularly important. Outbreaks of coccidiosis in turkeys occur most often during colder, wetter months of the year, usually the spring and fall, but can occur at any time.

Older birds also at risk

Another point emphasized by Radu was that, contrary to popular belief, coccidiosis can have a negative impact on all phases of the growing cycle. It's not just a disease of young poults 3 to 10 weeks old. True, the peak of oocyst shedding usually occurs in turkeys between days 35 and 50. But, he says, several trials have shown that variable patterns of oocyst shedding take place much later, sometimes as late as 20 weeks.

In practical terms, it's nearly impossible to entirely eradicate coccidia from the growing environment. That being the case, most strategies for dealing with coccidiosis are aimed at maximizing control and, more importantly, minimizing losses.

One of the primary ways growers try to control coccidiosis is by the use of anticoccidials, either ionophores or synthetically manufactured chemical drugs.

Two ionophores are currently approved for use in turkeys: monensin and lasalocid. The chemical anticoccidials available for use are: halofuginone, zoalene, amprolium, and diclazuril.

"Unfortunately," says Radu, "no ideal or perfect in-feed anticoccidial - either ionophore or chemical "has yet been developed.

"Every drug that's available has drawbacks," he added. "In most cases the overuse of anticoccidials will eventually lead to development of organisms with decreased sensitivity to the drug. In other cases, the use of some anticoccidial drugs may be associated with a high level of toxicity, especially if they're used repeatedly."

Anticoccidials: The downside

Floor pen studies confirm efficacy

Similar results have been obtained in floor pen studies. In two trials, conducted in simulated commercial conditions, investigators assessed the efficacy of 1.0 ppm against mixed Eimeria species in turkeys infected with coccidia at 14 or 21 days of age.

As in the battery-cage studies, investigators concluded that fecal scores for coccidia in diclazuril-treated birds were statistically lower than in controls. Weight gains were improved in the medicated birds and mortality was significantly lower as well.

Results obtained in the floor pen and battery-cage studies have also been confirmed in field studies. At the Branson conference, Howell said even large doses of diclazuril "up to 10 ppm fed for 18 weeks "didn't produce any negative clinical signs in birds. That included indices of overall clinical signs, measurements of body weight, feed conversion, hematology, and histology.

Toxicity to non-target animals or environmental toxicity can sometimes be an issue with various types of anticoccidials, especially chemicals. However, Howell reported that neither of those problems appeared to be associated with this new-generation anticoccidial, diclazuril (Clinacox).

Studies in which various non-target animals "ducks, horses, rabbits, dogs, cattle "were experimentally fed diclazuril produced no adverse effects in any of the species studied. Nor, said

Dr. Howell, do studies show that diclazuril will produce any adverse environmental effects if it's released into the environment under normal poultry feed practices.

Vaccination: A refined strategy

Meeting the coccidial challenge

Phillips explained that when poults in a brooder house are challenged by field strains of coccidia, without being treated by either in-feed anticoccidials or vaccines, levels of coccidia spiral upward above the desirable performance threshold resulting in clinical coccidiosis (Figure 1).

Though the disease is self-limiting and is usually resolved by the time the birds are moved to grow-out houses around day 35, it nonetheless can take a significant toll on overall health of the birds and resultant growth rates.

"When ionophores are used to control coccidiosis (Figure 2) the birds are challenged by the cocci, but at a reduced rate," Phillips explained. Ionophores allow cocci to go through cycling, and that helps build immunity.

But, Phillips points out, ionophores slow down the process and levels of cocci aren't always back down to riskfree levels when the birds make their move to the grow-out house.

"And those first few days in the grow-out house are critical," Phillips added. "It takes birds up to 2 weeks to acclimate to the new environment and to establish a new pecking order.

During that time, their immune systems are suppressed due to the increased level of stress, and that may give the cocci an opportunity to rebound." Chemical anticoccidials produce still another result (Figure 3).

"Effective chemical anticoccidials clear the gut entirely of susceptible organisms, and leave it open for the less sensitive strains," Phillips explained. "So if you use chemicals for several cycles you'll see substantial resistance developing by the third or fourth time around."

Vaccines: The ideal option for turkeys

What about vaccines?

Phillips said they're ideal for use in turkeys. One reason is that the growth cycle in turkeys is considerably longer than for other fowl.

"That gives them more time to catch up on any growth they may have lost due to the challenge of the vaccine," Phillips said. "You give the vaccine on day one," says Phillips. "You then have 21 to 28 days to build immunity"

(Figure 4). You've given a controlled dose, so the coccidial exposure is mild, well below the performance threshold. And by day 28 the cycling is complete." The birds then have a week to fully recover from the subclinical infection before they're moved to the stressful environment of the grow-out house.

Radu told producers about some of the results obtained using Coccivac-T, a live-oocyst coccidiosis vaccine especially formulated for use in turkeys.

In one trial, results using Coccivac-T were compared with those achieved using lasalocid (Avatec), an ionophore anticoccidial. About 300 poults were involved in the study "half were administered Coccivac-T, the other half lasalocid.

Neither group of birds showed evidence of clinical coccidiosis at any time during the trial. However, Radu stated that there was one important difference between the two treatment groups - performance.

"The Coccivac-T birds weighed significantly more than the hens that received Avatec (16.44 lbs compared with 16.04 lbs, respectively)," he said. Mortality in both groups of birds was very low.

Coccivac-T versus monensin

In another trial, Coccivac-T was evaluated in comparison with monensin (Coban). More than 1,100 birds were in each treatment group. One treatment group was vaccinated with Coccivac-T at the hatchery via spray cabinet application. The other treatment group received monensin in the feed continuously for 12 weeks. After 12 weeks, the monensin was discontinued and both treatment groups were put on a regimen of virginiamycin for the remaining 6 weeks.

"At the conclusion of the 18-week study," Radu told attendees, "both groups had performed well and there was no statistically significant difference in performance between the groups."

One important advantage of vaccination, Radu said, is that it can be used continuously in flock after flock or in a rotation program with anticoccidials.

"When used in a rotation program it has the benefit of seeding down the litter with highly sensitive oocysts," he added. "And that's a big plus. It results in dilution or displacement of any resistant strains that may be present. When the switch is made to an in-feed anticoccidial, it's likely to be more effective."

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