Overberg Research Projects. I. The epidemiology of parasitic nematodes in ewes, suckling lambs and weaners.

Total differential warm counts were done on sheep slaughtered from 7 May 1987 to 19 May 1988 at Boontjieskraal Estate in the Overberg, Republic of South Africa. It was found that winter lambs became infested with Nematodirus spathiger at 5 to 7 weeks of age. At weaning in October 1987 this species was superseded by Teladorsagia circumcincta and Trichostrongylus rugatus. Small numbers of Trichuris skrjabini and Oesophagostomum venulosum were also present. From July to October, 3rd and 4th stage larvae exceeded adult Teladorsagia in ewes, and from July to December 1987 and in May 1988 in lambs and weaners. Juveniles exceeded adult Nematodirus in ewes from July to October 1987 and in suckling lambs in July 1987 and May 1988. Infective larvae aestivate in the faeces or in the soil of the lucerne pastures in the dry, hot summer months and migrate on to the herbage during the cool, wet autumn. Grazing in summer on wheat stubble and even newly sprouted lucerne is safe, in paddocks ranging from 40 to 60 ha in extent, despite massive daily contamination by weaners with more than 60 million worm eggs. Previously infected weaners underwent spontaneous cure within 6 weeks to 6 months of starting to graze safe pastures, Teladorsagia being reduced by 77 to 98%, Nematodirus by 9 to 94% and Trichostrongylus by 34 to 40%.