Comparative Pathogenicity in Ovis aries of Homologous and Heterologous Strains of Haemonchus (Nematoda: Trichostrongylidae) from Domestic and Wild Sheep

Abstract

The comparative pathogenicity in domestic sheep of three strains of Haemonchus, one from the Barbary sheep (Ammotragus lervia), one from bighorn sheep (Ovis canadensis mexicana), and one from domestic sheep (Ovis aries), was evaluated in two experiments involving a total of 27 worm-free lambs. In each experiment the lambs were divided into four groups; each of Groups 1 to 3 was inoculated per os with one of the three strains of larvae while the fourth served as an uninfected control group. Equal numbers of infective larvae were given to each of the three infected groups within an experiment. Weight gains, feed consumption, hemoglobin levels, and helminth egg production were determined weekly. At the termination of the experiments after 74 and 77 days the lambs were examined post-mortem and the worms were counted. More severe haemonchosis resulted from the infections produced in domestic lambs by the homologous strain than by either of the heterologous strains of the parasite.