Abstract

The age at which permanent incisor teeth came into wear was recorded in 23 yearling flocks that differed in breed and management, and one mixed-age flock, of spring-born sheep. In female yearling flocks the first pair of incisors came into wear at a median age of 15 months, with a normal range of 13 to 17 months. Variation within flocks was seven times greater than between flocks. Teeth erupted 21 days earlier in male lambs than in half sib sisters. Time of eruption was not affected by lamb breed, date of birth or growth path. Data from the yearling flocks identified a substantial pool of animals older than 12 months of age that did not have two incisors in wear. These animals could be given dispensation for grading as lamb after the normal cut-off date if incisor teeth in wear is accepted as the cut-off criterion. This would help overcome the shortfall in supply of lean, heavy carcasses that occurs each spring before new season's lambs reach suitable size. In the mixed age female flock, the median ages when 2, 4, 6 and 8 incisors came into wear were 15, 23, 30 and 42 months. Later pairs of incisors came into wear earlier than commonly assumed and individuals with the same number of incisors varied in age by up to two years. These findings highlight substantial limitations to the use of number of incisors for determining age in sheep.

TW, Knight, SG Kannegieter, and GJ Hamilton

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 265-270, 1989