Experimental cross-infections of Haemonchus placei (Place, 1893) in sheep and cattle.

To examine effects on biology and morphology, Haemonchus placei infections were propagated in cattle or sheep and infective larvae were introduced into the same or opposite host. Ovine source larvae had a geometric mean (GM) prepatent period of 26.5 days regardless of host species, compared to 30.6 days for bovine source larvae regardless of host species. Similarly, ovine source H. placei had a higher GM percentage establishment versus bovine source larvae (9.6% versus 3.4%) regardless of host species. The patent daily egg count for ovine source versus bovine source H. placei was 109.1 versus 50.0 FEC regardless of host species. Mean spicule length for ovine source H. placei was 492.5 microm while bovine source measured 496.5 microm. Mean female tail length for ovine source H. placei was 586.5 and 589.5 microm for bovine source H. placei. Using synlophe morphology, all worms that were measured were identified as H. placei. Sixty-three percent of females examined for vulvar flap morphology had knob-like vulvar flaps while the remaining 37% had linguiform vulvar flaps.