Repeatability of seasonal wool growth in Merino Sheep

R.M.W. Sumner, J.N. Clarke, A.J. Pearson, P.M. Speedy

AgResearch, Whatawhata Research Centre, Private Bag 3089, Hamilton, New Zealand

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

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.

Keywords: NZSAPAB; Merino; wool; seasonality; repeatability