Abstract

This study was designed to test the hypothesis that elevated maternal thyroid hormone concentrations in mid- pregnancy are responsible for the observed differences in lamb follicle characteristics as a result of mid-pregnancy shearing. The study involved 51 twin-born lambs in a 2 x 2 factorial design involving dams that were either shorn or unshorn in mid pregnancy and had either normal or elevated thyroid hormone levels. All ewe groups were thyroidectomised except for unshorn-normal ewes which were sham-operated. The thyroxine implant and injection regimes used to manipulate maternal thyroid hormone levels in mid-pregnancy were successful in mimicking the levels previously reported in mid-pregnancy shorn ewes. Lambs born to shorn dams had significantly (P<0.05) higher coefficients of variation of mean fibre diameter. Dam shearing treatment had no effect on any other follicle or wool characteristic. Lambs born to ewes with elevated thyroid levels in mid-pregnancy had a significantly (P<0.05) higher numbers of secondary fibres, and tended to have more primary fibres (P=0.08) and whiter wool (P=0.06). The absence of any dam shearing-treatment effect on secondary and primary fibre numbers, fibre diameter and length, suggests that the changes observed in follicles and wool characteristics of lambs born to mid-pregnancy shorn dams are primarily due to elevations in maternal thyroid hormone levels in mid-pregnancy. More work is required to confirm this hypothesis.

PR, Kenyon, RG Sherlock, and ST Morris

Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 272-276, 2004