SUMMARYThe role of antibody in the resistance of sheep to infection withTaenia hydatigenametacestodes was examined using passive transfer of immunoglobulin. The immunoglobulin either was experimentally transferred in serum, or was transferred from immune ewes to their new‐born lambs in colostrum. Pooled serum from donor lambs which had received one, light, oral infection did not protect recipients although the donors themselves were immune. However, transfer of pooled serum from donors which had either received three oral infections, or three immunizations with solubilizedT. hydatigenaoncospheres in a water‐in‐oil adjuvant, resulted in 70–80 fewer cysts in the recipients. Colostrum from ewes infected with three high or low doses ofT. hydatigenaeggs was transferred to their lambs. A short acting protection (one to three weeks) was observed in the lambs. Comparisons by ELISA and Western blot, of the anti‐T. hydatigenaoncosphere antibody content of the donor sera, the sera of the recipients collected 24 h and seven days after transfer, the sera of the lambs and ewes, and the colostrum of the ewes, indicated that resistance to the challenge infection depends upon a critical level of
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