Producers looking for ways to improve bird performance and their bottom lines were advised to put more emphasis on routine monitoring of coccidial patterns in their flocks.

“Sometimes what’s not seen can hurt,” said parasitologist Dr. Steve Fitz-Coy. Without monitoring, coccidiosis could be taking a serious but unrecognized toll.

As it is now, many poultry producers put coccidiosis control on the back burner — until it becomes a problem. In the meantime, performance may suffer and dollars are lost, said Fitz-Coy, of Intervet/ Schering-Plough Animal Health.

In addition to monitoring coccidiosis patterns, he encouraged producers to avoid choosing the least expensive coccidiosis-control program. It’s understandable, considering the rising costs of production, but what might initially seem less costly may not be the most cost-effective over the long-term.

Coccidiosis, Fitz-Coy emphasized, is a dynamic disease and the patterns may change. That’s why monitoring is important. It can reveal trends within a poultry operation that tell producers whether a coccidiosis-control program is working or that it needs to be modified.

Coccidia, which are present in virtually all commercial poultry houses, can cause tremendous destruction of bird tissues, which leads to impaired food intake, digestion and absorption. The result is weight loss, poor feed utilization, poor pigmentation and even mortality, he said.

The damage caused by coccidial organisms is directly related to the number and species of Eimeria ingested, he said.

Controlling coccidiosis requires maintaining a low parasite burden, which is accomplished by keeping the coccidial intake and replication rate low, which in turn results in minimal cell destruction and less impact on bird performance, Fitz-Coy said.

Complicating the issue is the development of drug tolerance or drug resistance to the in-feed anticoccidials that producers have relied upon for so long, he continued.

“Rotation of drugs alone to combat drug tolerance or resistance is futile,” Fitz-Coy said. Successful coccidiosis control may require rotating multiple in-feed anticoccidials in conjunction with live, effective vaccines. He also recommends routine necropsy sessions, regular testing for drug responsiveness with anticoccidialsensitivity testing (AST) and conducting regular oocyst counts from litter or droppings, he said.

Fitz-Coy noted that several monitoring options are available and each has its own positives and negatives. Using a combination of methods consistently will provide useful and reliable data.

He cited examples from three different commercial poultry operations in different regions of the US to underscore his point that monitoring the pattern of coccidia and coccidiosis change is crucial.

In one complex, for example, necropsy data over several years showed that the prevalence of Eimeria acervulina, E. maxima and E. tenella was 33%, 45% and 9%, respectively.

During the early years, E. acervulina was more prevalent than E. maxima (see Figure 1). But with the use of certain anticoccidials during summer months, the prevalence of E. maxima increased and remained fairly high.

In the winter months, the prevalence of E. acervulina trended downward and appeared to be associated with the use of a specific in-feed anticoccidial. The AST data were in agreement with the findings from necropsy data, leading to changes in the coccidiosis program and improved coccidiosis control.

Which species is it?

Identifying which coccidial species is affecting flocks is an important part of the coccidial-monitoring process, Fitz-Coy emphasized in a second presentation at WPDC. He compared coccidia to zebras, which appear the same at first glance, even though each species is significantly different from the other.

“It’s the same with coccidia. Each species is unique, has unique pathology and pathogenicity and even drug responsiveness,” he said. Each species also must be treated as unique to achieve good coccidiosis control.

Features that differ among various Eimeria include fecundity — the ability to produce oocysts (eggs) — the region of intestine that each species parasitizes and the depth of parasitic development in the mucosa. Different species of Eimeria also vary in the size of their coccidial-endogenous (developmental) stage. The pathogenicity is influenced by these various characteristics, Fitz-Coy explained.

Eimeria praecox has relatively high fecundity but is a shallow invader of the mucosa and produces relatively small endogenous stages, he continued.

E. tenella has moderately high fecundity, is a deep invader of the mucosa and the endogenous stages are large. E. necatrix is a poor oocyst producer but is a deep invader with relatively large endogenous stages.

Because of these traits, E. praecox is considered non-pathogenic, while E. tenella and E. necatrix are highly pathogenic to chickens, Fitz-Coy said.

E. brunetti, E. maxima and E. mivati also develop deep into the tissues. Mature stages damage blood vessels, which results in bleeding into the intestinal lumen, he said.

Coccidial species that have a longer pre-patent period tend to be more pathogenic than those with shorter periods. The pre-patent time is how long it takes for the first appearance of oocysts in the feces of chickens after they are infected with Eimeria, and this pre-patent time can be used to help differentiate various species of Eimeria, he said. E. praecox has the shortest pre-patent period — 84 hours — compared to 138 hours for E. necatrix.

Another way to differentiate Eimeria species is by their size and shape when viewed under a microscope, although it can be challenging and requires someone skilled at the art of oocyst identification.

The oocysts of E. mitis, for instance, are almost round, and the oocysts of E. maxima are large and have a tint of color. The size and shape of the nonpathogenic E. praecox can be hard to tell apart from E. tenella, E. necatrix and even E. brunetti.

Advanced procedures such as polymerase chain reaction (PCR) can be useful but may not be able to identify all Eimeria species, Fitz-Coy said.

“The best approach for differentiating various species of coccidia may be using multiple methods of identification, such as parasite biology as well as PCR,” he said.

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