Differentiation of Eimeria species infecting sheep during the grazing season on permanent and new pastures under Norwegian conditions.

The total and differential oocyst counts of the different Eimeria species in the faeces of Norwegian ewes and lambs were investigated at weekly intervals during the grazing period on permanent and new pastures. The total oocyst counts of lambs on permanent pastures were significantly higher than those on new pastures 3–6 weeks after the beginning of the grazing period. This demonstrates that the oocysts had survived the winter in the pasture. Species differentiation indicated that E. ahsata, E. arlongi, E. crandallis, E. ninakohlyakimovae, E. faurei and E. parva are able to survive the winter in the pasture. E. crandallis occurred in the greatest numbers, and this species might be an important contributor to the clinical symptoms which are frequently observed in Norwegian lambs about 2–3 weeks after the beginning of the grazing period. There were on the other hand, indications that E. pallida has little ability to survive the winter in the pasture. The results were generally similar for most of the species during 2 successive years. The total number of oocysts in the faeces of ewes was low on new as well as on permanent pastures, and the species differentiation showed negligible differences. Consequently, it was concluded that the ewes could not be the source of the high oocyst numbers in lambs on the permanent pastures.