Immunization of lambs against Oesophagostomum columbianum, using irradiated third stage larvae.

The effect of gamma irradiation at doses of 40- and 50 kR on the development of third stage larvae of Oesophagostomum columbianum and the protection conferred by these irradiated larvae against the nematode, was studied in 6-8 week old male Kashmir Merino lambs. At 40- and 50 kR doses, the third stage larvae failed to develop to the adult stage in the intestine. Though single vaccination with 2000, 50 kR irradiated larvae failed to protect the animals against the infection, vaccination with the same number of 40 kR irradiated larvae conferred a partial protection. The presence of adult worms of O. columbianum in sites outside the intestine of 6-8 week old lambs have been demonstrated for the first time.