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The effects of short-term manipulation of thyroid hormone status coinciding with primary wool follicle development on fleece characteristics in Merino sheep

Published online by Cambridge University Press:  18 March 2011

M. L. McDowall ,
N. M. Edwards  and
P. I. Hynd
M. L. McDowall*
Affiliation:
School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy South Australia 5371, Australia
N. M. Edwards
Affiliation:
School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy South Australia 5371, Australia
P. I. Hynd
Affiliation:
School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy South Australia 5371, Australia
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Abstract

Thyroidectomy surgery performed late in gestation results in perturbations in wool follicle development in foetal sheep, showing the importance of thyroid hormones for wool follicle development. The aim of this study was to determine the influence of transient manipulation of thyroid hormone status at a time corresponding with foetal primary wool follicle initiation. Pregnant Merino ewes (n = 12 per treatment) were treated daily between gestational days 55 and 64 with control (vehicle), exogenous thyroxine (T4) or propylthiouracil (PTU), an inhibitor of T4 synthesis, and conversion to the active form of the thyroid hormone (triiodothyronine). There were no significant differences in birth weight, gestational lengths and birth coat scores of the resultant lambs. The total primary and secondary follicle densities were significantly lower in lambs exposed to exogenous T4 compared with other treatments (P < 0.05). However, the T4 group displayed a higher proportion of mature secondary follicles (reflected by increased mature secondary follicle densities and mature secondary/primary follicle ratios) than the other treatment groups (P < 0.05). The skin morphology of the lambs differed 12 months later, with the T4 group having significantly higher total follicle densities compared with the PTU group, largely attributed to increased mature and total secondary follicle densities. However, this increase in wool follicle densities did not translate to differences in the fleece yields and weight, fibre diameter, staple lengths or any other fibre parameters. This study showed that transient manipulation of thyroid hormone status during foetal primary follicle initiation does have long-term consequences on the morphology of wool follicles, in particular the maturity of secondary wool follicles.

Keywords

wool folliclesheepthyroid hormoneswool follicle developmentfoetal development
Type
Full Paper
Information
animal , Volume 5 , Issue 9 , 05 August 2011 , pp. 1406 - 1413
Copyright
Copyright © The Animal Consortium 2011

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