Failure to vaccinate lambs against Haemonchus contortus with functional metabolic antigens identified by immunoelectrophoresis.

Metabolic products from Haemonchus contortus larvae cultured in vitro from the infective third to fourth stage were collected and concentrated. Chromatographic and immunoelectrophoretic analyses were made to study the numbers and activity of antigens in the metabolic products derived from the in vitro cultured larvae. Three-month-old lambs were given a series of injections of metabolic antigens with and without adjuvant at dose rates of 0·05, 0·5 and 5·0 mg antigen protein per injection. These animals and saline injected controls were each challenged with 3000 H. contortus infective larvae after the last antigen injection and killed 35 days later. No difference was seen in the faecal worm egg counts or the differential worm counts among the vaccinated and control animals. The antigen preparation of worm metabolic products conferred no resistance to challenge infection with the parasite.