The response of breeding doses to nematodiasis: segregation into "responders" and "non-responders"

Responder and non-responder does were identified from a flock of 95 Scottish cashmere 2-6 year-old does exposed to natural nematode infection over a 12-month period. Every 5 weeks, the does were faecal sampled for worm-egg counts prior to anthelmintic treatment. Responsive and non-responsive individuals were identified on the basis of their cumulative faecal egg count (FEC) rankings: the 8 lowest and 8 highest rankings were deemed to be responders and non-responders, respectively. Retrospective analysis showed that the mean egg count of the 8 responders was significantly lower than that of the 8 non-responders. The selected responders and non-responders were subsequently housed together with 8 randomly selected does from a control line, and given a mixed trickle challenge with Teladorsagia circumcincta and Trichostrongylus vitrinus larvae (L3). Mean responders FEC was significantly lower following artificial infection than that of non-responder and unselected does. Peripheral eosinophilia was significantly greater in responders in the first 3 weeks of this infection. On day 60, the infection was terminated with anthelmintic and 7 days later the goats were given a single challenge of 50,000 T. circumcincta L3. The mean responder worm burden was lower, and exhibited greater evidence of retardation of worm development, than those of non-responder and unselected does. Responders had significantly more mast cells and globule leukocytes post-challenge than did the other 2 groups. These results suggest that under the conditions encountered in this experiment, it is possible to segregate goats into responders and non-responders using simple parasitological criteria, as individual responsiveness is a relatively repeatable phenomenon.