Eimeria alabamensis coccidiosis in grazing calves: control by a long-acting baquiloprim/sulphadimidine bolus.

The excretion of Eimeria oocysts, the faecal dry matter and the weight gain of three groups of 12 calves, were compared during their first 20 days of grazing on a pasture known to have been contaminated with oocysts of Eimeria alabamensis during the previous year. On the day of turnout (day 0) the calves in group 1 were each treated with one bolus per 200 kg bodyweight containing 1.6 g baquiloprim and 14.4 g sulphadimidine. The calves of group 2 received the same treatment on day 3, and the calves of group 3 were left untreated. Eleven of the untreated calves developed clinical coccidiosis due to E. alabamensis and excreted more than 850,000 oocysts/g of faeces 8-10 days after turnout. Seven of the calves in group 1 and five of those in group 2 developed diarrhoea, but it was milder and/or less persistent than in the untreated calves. The treated calves excreted significantly fewer oocysts and lost significantly less weight than the untreated calves. On day 21 all the calves were housed and on day 27 they were challenged with 10 million sporulated oocysts of E. alabamensis and turned out on to the same pasture. Only minor clinical signs were observed in some of the calves, indicating development of immunity in all groups. However, there was a tendency for the calves treated on day 3 to excrete more oocysts and to gain less weight than the other calves.