FIELD STUDIES OF THE IMMUNIZATION OF LAMBS WITH DRUG-ABBREVIATED INFECTIONS OF TRICHOSTRONGYLUS-COLUBRIFORMIS AND OSTERTAGIA-CIRCUMCINCTA

Fifty, 5-6 month-old lambs were randomly allocated to five equal group s. Three groups of lambs were immunised by three oxfendazole-abbreviat ed (artificial) infections of Trichostrongylus colubriformis and Oster tagia circumcincta. Group 1 was immunised with a high dose of larvae, Group 2 with a medium dose and Group 3 with a low dose. A fourth group was treated with oxfendazole only and a fifth group was not treated ( control). All groups were grazed together on pasture naturally contami nated with nematode larvae. Immunisation significantly reduced the num ber of eggs per gram of faeces in all three groups, but the lowest fae cal egg count was seen in Group 3 (immunised with the lowest number of larvae). Significantly better liveweight gains and wool weight were o bserved in Group 2 animals than in the control group. Of all anthelmin tic-treated animals, only Group 1 lambs did not have a significantly l ower dag weight than controls.