Abstract
Successive pairs of approximately 4-month-old Friesland bull calves, raised under worm-free conditions, were exposed to helminth infection for 14 days on dry-land Kikuyu grass pastures at 28-day to monthly intervals, on a coastal farm in a non-seasonal rainfall region of the Eastern Cape Province. With the exception of one pair of calves exposed for 28 days, this procedure was repeated for 28 consecutive months from December 1982 to March 1985. The day after removal from the pastures one calf of each pair was slaughtered and processed for helminth recovery and the other 21 days later. Both members of the last four pairs of calves were killed 21 days after removal from the pastures. Sixteen nematode species were recovered from the calves, and infection with Ostertagia ostertagi was the most intense and prevalent, followed by Cooperia oncophora. The calves acquired the greatest number of nematodes from the pastures from June to October of the first year and from June to August of the second year of the survey. Few worms were recovered from the tracer calves examined from November or December to March or April in each year of the survey. The seasonal patterns of infection with Cooperia spp., Haemonchus placei, Nematodirus helvetianus, Oesophagostomum spp., O. ostertagi and Trichostrongylus axei were all similar and were negatively correlated to atmospheric temperature and evaporation. Slight to moderate arrest in the development of fourth stage larvae occurred from July to September in Cooperia spp., April to July in H. placei, and August to October in O. ostertagi and Trichostrongylus spp. during the first year of the survey. Too few worms were present in the second year to determine a seasonal pattern of arrest. Species survival during the hot and windy summer months appeared to be achieved via a combination of arrested larval development and an ageing residual population of adult worms in the host, and a small extant population of infective larvae on the pastures.
Highlights
During the past 40 years large tracts of land along the southern coast of the Eastern Cape Province, South Africa, stretching from approximately East London (33°01’ S, 27°53’ E) in the east to Humansdorp (34°02’ S, 24°46’ E) in the west, have been planted to Kikuyu grass (Pennisetum clandestinum)
After removal of the representative samples from the processed ingesta of the day 21 tracer calves the remainder of the small intestinal contents was examined macroscopically for cestodes and that of the large intestine for adult Oesophagostomum and Trichuris species. This was not done for the day 0 tracer calves as their helminths were still immature and difficult to see with the naked eye
With the exception of September 1983 when large numbers of larvae were collected from the herbage and large numbers of helminths were recovered from the tracer calves, the numbers of nematodes in the tracer calves did not match the seasonal
Summary
During the past 40 years large tracts of land along the southern coast of the Eastern Cape Province, South Africa, stretching from approximately East London (33°01’ S, 27°53’ E) in the east to Humansdorp (34°02’ S, 24°46’ E) in the west, have been planted to Kikuyu grass (Pennisetum clandestinum). This is a temperate zone with frost-free winters and Parasites of domestic and wild animals in South Africa. The ixodid ticks recovered from the survey animals have been reported separately (Horak 1999)
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