EVIDENCE FOR THE EXISTENCE OF A SHEEP AND A GOAT LINE OF TELADORSAGIA-CIRCUMCINCTA (NEMATODA)

Populations of Teladorsagia circumcincta harbored by sheep and goats w ere investigated by means of isoenzyme electrophoresis. Genetic charac terization of 16 natural goat populations was based on 5 polymorphic e nzymes. Malate dehydrogenase (MDH-1) was the most informative; it had three alleles, the electrophoretically fast migrating one being named sR. We distinguished three groups with presence to over 20%, low frequ ency, and absence of sR, respectively. In four sheep flocks, only the third group was found. Neither of two laboratory reared lamb populatio ns originating from two geographic origins presented this third allele . When populations of worms with high sR frequency were passaged into lambs, a steep decrease in the sR-allele frequency was recorded, which was no longer demonstrated in lambs after the third passage. We sugge st that the worms lacking the third allele belong to the sheep line an d that those with the sR allele belong to the goat line. Thus, goats w ould be infected with worms of both goat and sheep lines, whereas shee p would harbor only the sheep line.