Nematode parasite populations in sheep on lowland farms I. Worm egg counts in ewes

Details are given of worm egg counts carried out on faeces from ewes during 1950–3. 2. Two periods of high egg counts were recorded each year; one during spring and the other in late summer. 3. The first increase appeared to correspond to the spring rise of other workers. It has been shown to be of short duration in each individual ewe, and the time of its occurrence directly related to the time of lambing. 4. Details are given of the seasonal incidence of different species of nematodes. 5. The spring rise is discussed and a theory is advanced to account for the phenomenon. It is emphasized that the fall in egg counts after the rise is as important as the increase. 6. A suggestion that the summer rise is spurious and caused by a reduction in volume of faeces passed during the first week after weaning is accepted.