Morphological types in Haemonchus contortus (Nematoda) populations in Ontario sheep

Abstract

Populations of Haemonchus contortus in 40 sheep near Guelph, Ontario, were examined for the prevalence of various vulvar cuticular processes. The sheep were submitted to the Ontario Veterinary College for necropsy from April to September in each of the years 1968 to 1972. More than 74% of the adult female worms in each sheep were "smooth" or without a vulvar process. "Knobbed" (with a knob-like projection), and "linguiform" (with a pendulous expansion or flap) types consisted of no more than 9 and 20% of the population respectively. There was no seasonal variation between these major morphological forms, but there was a seasonal trend in subgroups of the "linguiform" type.