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Dr. Linnea Newman

Good coccidiosis control and consistent flock performance can be achieved flock after flock, but house conditions and management need to be considered to get the best results, said Dr. Linnea Newman, a consulting veterinarian for Intervet/Schering-Plough Animal Health.

“Coccidiosis is a dynamic, fluid process within the chicken house that can be affected by flock density, litter moisture, in-feed anticoccidials or vaccination,” Newman said.

Coccidial-oocyst output increases with each sequential life cycle after birds become infected. When bird density is higher, so are litter moisture, coccidial multiplication and the coccidial challenge, she said.

What this means regarding coccidiosis control, she said, is that in-feed anticoccidials have a greater challenge in higher density, small-bird systems. Conversely, lower bird density means less moisture in the house and less oocyst multiplication. Chicks also produce less litter moisture than older birds, so that when in-feed anticoccidials are used, the challenge generally tends to peak later in the life of a broiler flock.

Climate and ventilation are other factors that affect litter moisture. Winter is often a time of low ventilation, higher house moisture and higher coccidiosis challenge. Thus, we tend to see more coccidiosis challenge during winter and early spring, and infeed medications don’t perform as well, Newman said.

Litter moisture is also a function of litter material and depth. Deep wood shavings can act like a sponge, while thin litter leaves nowhere for moisture to go. Straw can mat at the surface, holding moisture at bird level. Higher moisture translates into more coccidia.

“Look at the litter style and management in your poultry houses and try to understand how it will affect the success or failure of coccidiosis control,” she said.

Control with anticoccidials

In-feed anticoccidials, Newman continued, work by suppressing the coccidial life cycle.

The goal with a chemical anticoccidial is to completely suppress the coccidial life cycle, but only resistant strains survive to reproduce and the bird does not develop immunity against coccidiosis. “Resistance happens quickly,” she said. Ionophores reduce the coccidial reproductive rate but don’t stop reproduction. Coccidial populations will slowly build over time, and immunity is finally achieved if birds live long enough before slaughter. The immunity induced by ionophores may be incomplete since different coccidial species multiply at different rates.

A typical chemical-ionophore program has some oocyst leakage — oocyst shedding — but as long as the total oocyst count stays below 20,000 oocysts per gram at shedding’s peak, “I consider this to be good control,” Newman said.

When sensitivity is lost, however, the parasites have more multiplication in the intestine and more oocysts are shed in the feces. The peaks become higher with continued use of the same drug. “When this occurs, we must consider the interaction of coccidial leakage and environmental conditions. The leakage will occur late — after 28 days of age. And the degree of coccidial leakage will depend upon seasonal moisture conditions and stocking density. Control will fail most quickly in high-density, small-bird operations or during winter and early spring for any size bird,” she said.

Newman cautioned that when reduced sensitivity occurs, it is often not obvious to the producer. Birds can look perfectly normal and there are no typical signs of coccidiosis, no mortality nor even any abnormal feces.

“More of the coccidia are escaping the suppressive effect of the anticoccidial and they are reproducing. Oocyst peaks are higher and are usually delayed to 4 or more weeks of age. The result is decreased performance during the seasons when coccidiosis is more difficult to manage,” she said.

Control with coccidiosis vaccines

Broilers vaccinated against coccidiosis at 1 day of age shed oocysts 4 to 7 days after vaccination. The chicks then ingest and recycle the vaccinal oocysts, a process that initiates lifelong immunity against coccidiosis, Newman explained.

“Different vaccines, however, require a different approach to management,” she emphasized. For instance, the live-oocyst vaccine Coccivac-B for broilers contains mild, natural strains and initiates a pattern that’s similar to that which occurs with wild strains. Immunity in broilers from vaccination with Coccivac-B is complete after 3 to 4 Eimeria life cycles.

Full immunity after using Coccivac-B takes multiple coccidial life cycles. For instance, Eimeria acervulina and E. mivati produce massive numbers of oocysts and immunity develops quickly, while E. maxima has a lower reproductive rate and immunity can take 3 to 4 recontamination cycles to develop. E. tenella falls somewhere in between, taking about 3 recontamination cycles to develop full immunity.

Natural-strain coccidiosis vaccines, like Coccivac-B, result in mild lesions, and oocyst shedding peaks when stocking density is from low to moderate. In contrast, a precocious-strain vaccine used with low- to moderate-stocking densities may fail to cycle effectively enough to induce immunity before wild challenge levels can build. High stocking density and wet litter favor the coccidiosis life cycle, so Coccivac-B may produce moderate lesions and higher oocyst shedding peaks, while a precocious vaccine responds well to these conditions, she said.

This example demonstrates that with a live coccidiosis vaccine, “you can manage your immunity pattern,” she said (Figure 1). “You can drive immunity harder or reduce reactions, as needed, with management changes; the goal, ultimately, is to minimize the intestinal insult in broilers,” Newman said.

The moderate density pattern indicated in Figure 1 in gold is the more desirable pattern for achieving consistent and uniform performance. It is the easiest to manage from season to season, and it is sustainable once the pattern is established, she said.

Establishing an intentionally managed, early and mild lesion pattern is the best way to achieve uniform and sustainable performance that lasts for years, not just for one rotation.

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