A study of fibre diameter variability in Merino wethers

Abstract

Analysis of the relationship between fibre diameter distribution at an early age and the change in average fibre diameter over time was carried out on fleece samples from Merino wethers. The objective being to determine if fibre diameter distribution could be used as a predictor to identify animals which may experience micron "blowout". In the context of this study, micron "blow-out" is defined as a change in hogget average fibre diameter with increasing age of more than approximately 25 percent. The Lincoln University Wool Measurement Service holds production records and mid-side wool samples from animals in the Central Otago Merino Wether Trial (n = 267 in 1990). Data on each individual animal's average fibre diameter are available from 1984 to 1990 whilst mid-side wool samples are available for 1984, 1987, 1988, 1989 and 1990. Wool staples were randomly removed from the mid-side samples of 267 Merino wethers and their fibre diameter distributions measured using a Fibre Diameter Analyser (FDA). Distributions were obtained for 1984, 1987, 1989 and 1990 (n = 1068). Animals were ranked on the size of their fibre diameter distributions based on a calculated range value. The top 51 animals and the bottom 51 animals based on this ranking were identified, representing large and small distributions respectively. Regression analysis was used to determine the strength of the relationship between fibre diameter distribution and subsequent change in average fibre diameter. No significant correlations were found to exist for individuals within groups. When changes in average fibre diameter between 1984 to 1990 and 1987 to 1990 were averaged within groups for all individuals, the changes in average fibre diameter were significantly higher (0.05 < P < 0.001) for the large range groups than small range groups. The variability introduced into this study attributable to the methods of sub-sampling and the measurement methods employed were significant and may have masked a relationship between fibre diameter distribution and change in average fibre diameter over time. There is, as yet, insufficient evidence to support the use of fibre diameter distribution in Merino breeding and selection programmes. This study has found this to be especially true when the basis of measurement of fibre diameter distribution is for reducing the incidence of micron "blow-out".