Hornedness and polledness in sheep. II. The inheritance of horns in Merino ewes

Observations have been made on Merinos of the medium Peppin, medium non-Peppin, and strong non-Peppin strains. The appearance of true horns in ewes in a large medium Peppin flock has been shown to result from the action of a dominant autosomal gene designated P'. Both P'P' and P'p ewes grow horns approximately 5–12 in. long when adult, while pp ewes have either bone knobs or short, loose sours growing on their horn sites. The frequency of P' in one medium Peppin flock observed is 0.11. No expression of P' in the entire male has been demonstrated, possibly because of the great effect of the male sex hormones on horn growth in rams.