Wool samples were clipped from the midside of 27 Merino rams and 33 unmated Merino ewes born in 1990 at 4 or 8 weekly intervals, depending on the season, between July 1991 and January 1994. Wool growth rat and mean fibre diameter were measured. Both wool growth rate and mean fibre diameter exhibited seasonal growth cycles which were synchronous. The rhythm of the seasonal cycle for each characteristic was calculated as:- Rhythm (%) = (Max-Min) / ((Max+Min) / 2) x 100 The rhythm for wool growth rate exceeded that for mean fibre diameter while the rhythms for both characteristics increased significantly between the first and second year but not between the second and third years. Although wool growth rate and mean fibre diameter were strongly correlated between adjacent clipping periods, the derived rhythm estimates for both characteristics were only weakly correlated between years. Adjustment of the rhythm estimates for liveweight change during the same period significantly improved between sheep repeatability of the seasonality estimates. These data indicate that a significant proportion of the variation in both wool growth rate and mean fibre diameter was, after adjustment for liveweight change, associated with permanent phenotypic differences among the sheep in the rhythm of their seasonal wool growth cycle.

RMW, Sumner, JN Clarke, AJ Pearson, and PM Speedy

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 163-166, 1994
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