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Two extensive surveys conducted in Norway indicate the incidence of coccidia-infected broiler flocks has increased from 42% to 76% during a 3-year period.

In addition, three coccidia species predominated; one was relatively benign, but the other two were extremely pathogenic and were found in 77% and 25% of flocks.

“Twenty years’ use of the same type of coccidiostat in the broiler industry may have contributed to the increased incidence of coccidiosis on Norwegian farms,” says Anita Haug, who performed the surveys as part of her doctoral thesis.

The studies, conducted on broilers receiving in-feed narasin during 2000 to 2004, were published in the June 2008 issue of Avian Pathology and were the focus of a recent article on thepoultrysite.com.

Although the total parasite load countrywide did not alter significantly during the study period, there were large regional differences in the numbers of infected flocks, the level of infection and the dominant coccidial species, Haug found.

Parasite load alone was not a good measure of the economic significance of coccidial infection, but reduced production occurred when there were over 50,000 parasites per gram of feces and the pathogenic strains dominated. A corresponding level of infection with more benign coccidial strains did not have the same effect on production.

The surveys were funded by the Research Council of Norway; Haug performed her work at the National Veterinary Institute in Oslo and the National Veterinary Institute at Uppsala, Sweden. She developed new test methods by simplifying traditional ones, and also developed a “robust, effective and sensitive” molecular-biological test.

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