The seasonal incidence of gastro-intestinal helminths and of Oestrus ovis was determined by slaughter of successive groups of 4 tracer lambs, each exposed on pasture for 33 days.
Haemonchus contortus was present from March 1979 to early July 1979, with a generally increasing percentage of 4th stage larvae in each successive month. A "spring rise" in the egg count was seen in flock sheep in October 1978. Oesophagostomum columbianum was recovered from tracers slaughtered in March
1979. Apart from December and March, Moniezia spp. were present from November 1978 to early July 1979.
Oestrus ovis was active from September 1978 to early June 1979, with peak larval burdens recorded from
October to December and from April to early June.
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