Haemolytic effect of Pasteurella haemolytica on blood from young mammals

On agar plates containing young lamb blood, Pasteurella haemolytica produces a wide outer zone of partial haemolysis in addition to the narrow zone of complete clearing seen on adult sheep blood agar. To determine whether this phenomenon was limited to lamb blood, samples from young animals of 20 mammalian species were examined. Two species — the barbary sheep (Ammotragus lervia) and scimitar horned oryx (Oryx tao) — possessed blood that gave this effect provided that the samples were taken from young animals. The 18 species that gave negative results included an ovine species, the bighorn sheep (Ovis canadensis).