Studies of face cover in the New Zealand Romney Marsh sheep. II. The measurement of face cover and of factors associated with differences in face grades

Abstract

Face cover was measured as poll staple length and the length of the nose free of visible wool growth. Forty open-faced and 80 woolly-faced ewes were measured every June for five years. While differences in the measurements occurred between the grades, analyses showed that neither measurement, nor a combination of them, discriminated satisfactorily between grades over the full range of face cover. Within a face-cover grade, poll staple length was positively correlated with the midside staple length. Between the grades the relationship was a negative one. Follicle characteristics were measured in facial skin from seven open-faced and 10 woolly-faced sheep from the same flock. Open-faced sheep had the larger primary follicles but smaller secondary follicle diameters. Thus open-faced sheep had a dp/ds ratio of 2.3 and woolly-faced sheep one of 1.4. Further skin samples from six rams and seven wethers at 1 year of age showed that castration had reduced primary follicle diameter (57 and 41 µ) without changing the face cover. Also ewes and ovariectomized ewes showed a difference in SIP ratio on the face (1.9 and 2.5) with no difference in face cover. It was concluded that primary follicle size was not an immediate determinant of face cover but that factors external to the facial follicles were more likely to be of importance.