The effects of larval age and cold storage on the ecdysis of infective Haemonchus contortus cayugensis larvae

Abstract

Infective Haemonchus contortus cayugensis larvae were harvested from faecal cultures, cleaned and stored at 4°C. By means of small sample runs, exsheathment rates were determined for batches of clean larvae prior to and during storage. The larvae were stimulated to exsheath at 40°C in 0·02 m-Na2B4O7. 10H2O into which a gas mixture of 40% CO2–60% N2 was bubbled. A 20 and 60 min exsheathing time produced some and no decrease in exsheathment rates respectively for freshly cleaned unstored larvae and larvae stored 1–12 weeks. In all instances there was a reduction in the exsheathment rate 24 h after the larvae were placed in cold storage. This was considered a result of a cold shock from which the larvae did not recover until after the fourth day.