Field research has yielded unexpected findings about the impact of clean or used litter on coccidiosis control and underscores the importance of initiating coccidiosis immunity early in broiler flocks.

“Poultry producers, pay attention!” challenged Dr. Linnea Newman, a consulting veterinarian with Intervet/Schering Plough Animal Health. “Birds eat half their total feed in their final 2 weeks. With corn prices so high, you don’t want to give up feed-conversion efficiency and weight gain because of coccidiosis-linked production losses.”

The research that prompted these comments from Newman involved the collection of fecal samples from multiple broiler farms that were using a variety of coccidiosis-control programs. The sampling, which was done over time at farms in Canada and various US locations, has opened an interesting window into the dynamics of coccidiosis in commercial broiler operations.

Canadian broiler houses are required to do a complete cleanout between flocks to help manage viral challenges from diseases such as Newcastle, Marek’s and infectious bursal disease, Newman explained. In stark contrast, US broiler houses reuse litter. Broiler houses on the Delmarva Peninsula have litter that may be used for up to five years without cleanout, in part because environmental constraints prohibit dumping used litter.

The coccidiosis-management programs used on the various farms studied included both in-feed anticoccidials and vaccination programs, Newman said.

Contrary to expectations, the patterns of oocyst shedding on the Canadian farms showed a high and late coccidial challenge and even more so in lowerdensity flocks. Similar results have been seen on US farms that use clean litter, and it’s an unwelcome pattern when birds are changed to unmedicated withdrawal feed, she said.

In contrast, broilers on Delmarva farms that were raised at higher densities and on heavily used litter showed earlier and lower oocyst-shedding peaks.

Flocks in the US vaccinated year-round for coccidiosis produced an earlier oocyst peak on used litter.

Vaccinated flocks in Canada that were raised on clean litter produced oocyst peaks a week later than the vaccinated birds on used litter, but these peaks were still earlier and lower than what was seen in flocks using in-feed anticoccidials, Newman said.

Anticoccidials losing effectiveness

In an interview with Intestinal Health, Newman said the contrasting patterns she’s observed highlight two important realities about coccidiosis: In-feed anticoccidials are continuing to lose their effectiveness, and immunity plays a key role in controlling the timing and severity of oocyst peaks.

It was unlikely that Canadian producers were aware that coccidiosis was sapping productivity to the extent that it was. “This was a wake-up call for them,” Newman said.

The smartest thing a poultry producer can do to minimize late intestinal damage and maximize genetic potential is to transfer to a coccidiosis-vaccination program — either a year-round program or rotate a vaccine with anticoccidials to renew their sensitivity to the Eimeria strains that cause coccidiosis, Newman advised.

“Both strategies work, but year-round vaccination is probably a better option. It’s a paradigm shift that’s needed,” she said. “The only problem you can get with a rotation is that every time you rotate, you shift the pattern back to the late coccidial challenge that you get with in-feed anticoccidials.”

The high and late oocyst peaks of medicated broilers that are in houses cleaned out between flocks have exposed the growing ineffectiveness of anticoccidials used alone, Newman continued. “If you re-use litter, you get some natural vaccination from the oocyst populations shed by the previous flock, which helps stimulate immunity; if you have clean litter, you are wholly dependent on anticoccidials for control.”

She predicts the effectiveness of in-feed anticoccidials will continue to wane. Commenting on the recent reintroduction of the chemical anticoccidial clopidol in the US after a 15-year absence, Newman said it has been providing excellent coccidiosis control, but the resistance that originally forced it off the market will likely return.

“Some people are increasing doses of anticoccidials to extend the useful life of the product, but that strategy won’t last,” she warned. “Another approach is to use anticoccidials in the withdrawal feed to combat the late peaks. Again, this is likely to cause increasing resistance.”

Another way to extend the life of in-feed anticoccidials might be to follow the example of one large integrator in the US. “The company uses very low levels of anticoccidial and lets natural immunity through field exposure do the rest,” she explained. “The only problem with this approach is that we don’t know the nature of the incoming oocyst challenge. Is it more or less pathogenic? You never know.”

The ideal strategy — and this is the nub of Newman’s take-home message to growers — is to stimulate an early coccidial challenge in a controlled way, preferably through vaccination.

“Producers need to find out what their normal oocyst-shedding patterns are and also understand seasonal variations. One sample alone won’t do it — that’s just a snapshot. They need to see what happens during different seasons and during the different phases of a rotation program. I can guarantee you that most farm managers won’t be aware of these patterns,” she said.

Consistency, Newman concluded, is the name of the game. “Consistent feed conversion and weight gain performance, early immunity, avoiding late gut lesions — that’s what it’s about,” she added.

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