Response to transplanted adult Ostertagia ostertagi in calves.

Plasma pepsinogen levels became elevated in groups of recipient calves immediately after transplant with adult Ostertagia ostertagi. These rises occurred in both previously parasite-naive calves and in calves which had experienced prior infection terminated with an anthelmintic either seven or 21 days before transplant. From the results it appears that adult O ostertagi play a significant role in the elevated plasma pepsinogen levels associated with bovine ostertagiasis.