Parasites of domestic and wild animals in South Africa. V. Helminths in sheep on dryland pasture on the Transvaal highveld.

The seasonal incidence of helminth infestation on a farm in the Transvaal Highveld was determined by the slaughter of tracer lambs exposed on pasture for periods of approximately 6 weeks. Haemonchus contortus, the most prevalent nematode, was recovered in the greatest numbers from January--May 1974. Peak counts of Ostertagia circumcincta were made during March and April 1974 and in January 1975, while Trichostrongylus spp. were mainly encountered from March--June. Cooperia spp. were generally recovered from November--May and Moniezia expansa from October--April. H. contortus, O. circumcincta and Cooperia spp. all exhibited increasing degrees of arrested development in the 4th larval stage from February--June.