The effect of thyroxine implantation on wool growth

1. An experiment was carried out to determine the effect of L-thyroxine implantation upon the wool production and live-weight change of Corriedale and Suffolk × Border Leicester-Merino sheep. 2. Groups fed hay in restricted amounts gave approximately 12% more wool when treated with thyroxine. Since there was no change in fibre diameter, this was presumably due to an increase in staple length. 3. Groups fed hay ad lib. gave no significant increase in wool production when treated with thyroxine, nor did their rate of food consumption alter. Their level of wool production over the 5-month period was approximately the same as that of the thyroxine treated, restricted fed, sheep. 4. All thyroxine-treated groups lost approximately 10% of their live weight. This was in the nature of a steady decrease from the second to the seventh week after treatment. Live weights then remained at about the same level for a further 8–10 weeks when they commenced to return gradually to their original weights.