Effect of implanted testosterone propionate on the growth and wool production of Merino wethers

Abstract

The effect of subcutaneous implantation of testosterone propionate in fine-wool Merino wethers at pasture was studied in four experiments over a 5-year period. The wethers were maintained virtually free of posthitis so that the observed responses to implantation were physiological in origin. In nine comparisons two implants of 70 mg testosterone propionate per annum increased liveweights significantly. Annual greasy wool weights increased by amounts ranging from 0.03 to 0.25 kg per head, the differences being significant on five occasions. Annual clean wool weights increased by a maximum of 0.13 kg per head. Fleece weight indices used as a measure of the gross efficiency of wool production were similar in the implanted and control wethers in all experiments. Also no significant change in efficiency was recorded where direct measurements were made of wool grown and food intake. Implantation tended to reduce the percentage yield of clean wool, the effect being greatest in the first year of treatment. Measurement and assessment of wool traits of commercial importance showed negligible differences between treated and control wethers and the average value per kilogram greasy wool was similar.