A survey was conducted on chicken broiler farms from Romania in August-November 2010 to evaluate economic losses due to coccidiosis. Data were collected from six broiler farms of different capacity regarding chemoprophylaxis program, weight gain, feed conversion, and mortality, for two previous flocks in two houses of each farm, and finally we evaluated the economic losses. Also, faeces samples were collected and oocysts were classified according to their size, and virulence of each Eimeria

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... field isolate was determined by lesion scoring. Correlations between economic performance, oocysts category, and virulence of Eimeria were assessed by multiple linear regression. Total economic losses per 24 flocks of 18,000 chicks each were about €37,948.2, with an average of €3,162.4 per flock, and they were caused by mortality (34.8%) and poor feed conversion (65.2%). Poor body weight gain was associated with AM oocyst category (presumptively E. acervulina and/or E. mitis), high lesion score in the duodenum, and coccidiostat used for chemoprophylaxis. Feed conversion ratio was linked to the same parameters as body weight gain, minus chemoprophylaxis programme, plus total lesion score. The percentage of mortality was influenced by the lesion score in the caecum and total lesion score. Statistical analysis showed that epidemiological survey of broiler flocks during the grower period can help the farmer to avoid important economic losses due to coccidiosis. As in other countries, the economic losses caused by coccidiosis in Romania are important, and a good prophylaxis programme can reduce the economic impact of coccidiosis.