THE INFLUENCE OF A COOPERIA-ONCOPHORA PRIMING ON A CONCURRENT CHALLENGE WITH OSTERTAGIA-OSTERTAGI AND C-ONCOPHORA IN CALVES

The development of immunity to Ostertagia ostertagi and Cooperia oncop hora and interactions between these species were investigated in exper imentally infected calves. Parasitological, serological and histologic al parameters were used for assessing immune responses. No conclusive evidence of an effect of C. oncophora on the course of an O. ostertagi infection in calves could be shown. Following a challenge with C. onc ophora and O. ostertagi of C. oncophora primed calves, no significant reductions in establishment rate, faecal egg counts, worm length or th e percentage of early fourth stage larvae could be demonstrated. Resul ts also confirmed earlier work showing the very different degrees of i mmunity conferred following immunisation with either C. oncophora or O . ostertagi. While a protective immunity was generated in the case of C. oncophora, continuous infection of calves with 420000 L-3 of O. ost ertagi during almost 5 months induced immune reactions which affected growth and fecundity of the worms but not the establishment rate.