Exsheathed infective larvae (L3) of 16 species of nematodes were tested for infectivity in either sheep or cattle after they had been frozen and stored in 0,09% NaCl solution in the gas phase of liquid nitrogen for periods of up to 59 months. A mean of >90% of the L3 of Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus axei, Trichostrongylus colubriformis, Nematodirus spathiger, Oesophagostomum columbianum and Chabertia ovina of sheep and Haemonchus placei, Ostertagia ostertagi, Cooperia spp. (C. pectinata and C. punctata), Nematodirus helvetianus and Oesophagostomum radiatum of cattle was alive when they were thawed, after having been frozen for 52-59 months.
These L3 as well as those of Marshallagia marshalli and Trichostrongylus falculatus, which had been frozen for 30-33 months, were infective to sheep or cattle when dosed per os or inoculated into the abomasum or the duodenum. Thawed Dictyocaulus filaria L3, frozen for 31 months, developed poorly when injected intravenously into sheep. This appears to be the first report showing infectivity of L3 of O. circumcincta, T. colubriformis, N. spathiger and, possibly, of O. radiatum by the oral route after cryopreservation in liquid nitrogen.