Resistance dynamics of calves to infection with Trichostrongylus axei

Calves were immunized with 10 000 infective larvae each of Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus axei and challenged with 100 000 of each species. When compared with nonimmunized controls, the immunized calves had 95% fewer H. contortus, 10% fewer O. ostertagi, and 20% fewer T. axei; the latter two reductions were not significant. In four other experiments single or multiple immunizing inoculations of T. axei followed by challenge at various intervals after immunization failed to result in significant resistance measured by the number of worms of the challenge inoculation that became established, by post-challenge fecal egg count, and by gross pathologic alterations of abomasa at necropsy.