Individual variation and effect of priming dose level on establishment, growth and fecundity of Cooperia oncophora in re-infected calves.

We investigated the effect of bovine anamnestic immunity on a range of parasitological variables. To this end, calves were primed with a single oral dose of 30000 or 100000 infective larvae (L3) of Cooperia oncophora, drenched with anthelmintic, maintained worm free in the following 2.5 months and subsequently re-infected with 100000 L3. Parasitological profiles of low, intermediate, and high responders were compared. The reduction in establishment of the worms was shown by a lower worm burden and increased percentage of fourth-stage (L4) larvae. Worm length and fecundity were similarly reduced by both priming doses but, the speed by which the effect occurred differed between animals primed with 30000 or 100000 L3. The difference in establishment between the responder types demonstrates that the ability of intermediate responders to mount a more effective and faster immune response compared to low responders is sustained after secondary infection.