Description of Ostertagia ostertagi and Ostertagia leptospicularis hybrids in experimentally infected sheep.

Hybrids of Ostertagia ostertagi and Ostertagia leptospicularis, derived from experimental infections in sheep, are described. Morphometrics of the hybrids were intermediate between those of parental lines for a large range of parameters (distance from apex to cervical papillae and length of esophagus for males and females, length of spicules for males, and length of vestibule, distance from vulva to the end of tail, width of tail at anus). The morphological relationship between hybrids and their parent species was assessed by discriminant analysis based on the relative values of these parameters (actual value/length of the worm). Each parental line, either bred in sheep or in the natural host, was morphologically similar and differed from hybrids.