Of the 12 species of bovine coccidia, Eimeria zuernii and Eimeria bovis are the most familiar pathogenic species, however there is a third which is less well known – Eimeria alabamensis.
- Unlike the other two, E. alabamensis rarely causes clinical coccidiosis in housed calves although it may be present in small numbers
- This is important because immunity to coccidiosis is species specific and calves may not have developed good immunity against E. alabamensis by the date of turn out
- E. alabamensis oocysts take longer to reach the infectious stage (sporulation) and this doesn’t occur at temperatures below 15°C. In contrast E. zuernii/bovis will sporulate in 10 – 14 days at a temperature of 10°C
- A second difference is the time required after infection to complete their life cycle and produce oocysts. This takes 2 to 3 weeks for E. zuernii/bovis but for E. alabamensis the pre patent period can be as short as 6 to 8 days.
Outbreaks of severe watery diarrhoea have been reported within 1 to 2 weeks of turn out. Although mortality rates are usually low, morbidity is high, weight loss is rapid and calves can take a long time to regain condition. As with other coccidial infections diarrhoea can precede patency and continue after the peak of oocyst shedding. If coccidiosis is suspected it is useful to sample 2 to 3 calves as we often see a wide range of oocyst counts between individuals.
Oocysts are capable of overwintering on pasture so the risk of E. alabamensis outbreaks can be reduced by not turning out young stock onto the same fields each spring. Where the problem has previously been diagnosed, and grazing high risk fields is unavoidable, prophylactic treatment should be considered.