The use of irradiated larvae as immunizing agents in Haemonchus contortus and Trichostrongylus colubriformis infections in sheep

Abstract

Six of 10 lambs previously given two doses of irradiated (60 kr) Haemonchus contortus larvae showed solid resistance to an experimental challenge with 10,000 larvae. The remaining four lambs in the group developed moderate infections. Nine of 10 lambs previously given two doses of irradiated (80 kr) Trichostrongylus colubriformis larvae showed solid resistance to an experimental challenge with 30,000 larvae. The 10th lamb was moderately resistant. Doses of X-rays within the range 40–100 kr had no effect on the exsheathment of H. contortus in the rumen, but few male worms developed as far as the fourth stage. It seems likely that the irradiated males and possibly a significant proportion of the irradiated females are unable to complete the ecdysis from the third to the fourth stage.