Excretion of Eimeria oocysts in calves during their first three weeks after turn-out to pasture.

The numbers of Eimeria oocysts per gram (opg) and the dry matter content of 449 faecal samples taken from 54 calves in 8 herds in south west Sweden were determined during the last 2 weeks before and the first 3 weeks after the animals were turned out to pasture. While they were housed only between 0 and 580 opg were found and in 2 of the herds the numbers of oocysts remained low after turn-out. In the other 6 herds the numbers of oocysts increased after 8 to 10 days and reached a peak of between 1080 and 80,803 opg 9 to 18 days after turn-out. By 21 to 24 days after turn-out the opg-values had declined to their initial levels. Eimeria alabamensis accounted for most of the increase, but small numbers of oocysts of E. auburnensis, E. bovis, E. bukidnonensis, E. cylindrica, E. ellipsoidalis, E. pellita, E. subspherica, E. wyomingensis and E. zuernii were also observed. The interval between turn-out and the start of the increase in excretion of oocysts corresponded closely to the prepatent period of E. alabamensis and overwintered oocysts were therefore the most likely source of the infection. In 6 of the herds the dry matter content of the faeces of the calves decreased after turn-out and 56% of the calves had clinical diarrhoea. Although it cannot be excluded that change of diet may have contributed to these symptoms, E. alabamensis infection is suggested as a potential cause of diarrhoea and loss of condition in calves in Sweden during their first weeks on pasture.