Causes of variation in dental characters of Scottish Blackface sheep in a hill flock, and relations to ewe performance

Abstract

SUMMARYObservations were made in three successive years on the dentition of Scottish Blackface ewes of 1½–4½ years old in a large hill flock in southern Scotland.The number of permanent incisor teeth was not a reliable guide to age, since at each age there was variation about the modal number. The length of the central permanent incisors increased slightly with age, and associated with this there was a slight forward movement in the position at which these teeth occluded with the dental pad. The modal position was 1 mm behind the anterior point of the dental pad of gum. About 1·5 % of the observations had bite positions deviating by 5 mm or more from the mode.Keeping the females during their first winter on low-ground pasture instead of the hill led to earlier eruption and slightly longer central incisors, but had little effect on bite position.The heritability of the number of incisors present at any one age was estimated to be 0·39 ± 0·11 by paternal half-sib correlation and 0·80 ± 0·27 by daughter-dam regression. Estimates of h2 for incisor length were less than half these values and those for the measure of bite position were very small and not significantly different from zero.For the ages up to 3½ years old, there were low but statistically significant correlations of number of incisors with ewe live weight (0·1–0·2) and fleece weight (around 0·1), incisor length with fleece weight (around 0·1) and at 1½ years old only between the bite measure and both weights (0·1). Weight of lamb weaned by the ewe was uncorrelated with these dental traits.It is concluded that in this flock, culling on the dental characters studied would not have improved performance, and selection would not change the position of the bite.