A Comparison of the Performance of On-Farm OFDA2000 and In-Store FLEECESCAN - Part 1: The Precision of the Measured Fibre Characteristics of a Fleece

Abstract

A number of authors have reported that the precision of the measurement of a fleece will have an impact on the decisions taken on-farm with respect to sheep selection for on-going breeding or culling and fleece selection for preparing classed lines of wool of different Mean Fibre Diameter (MFD) for sale.

Determination of the precision of MFD for a fleece test has been the subject of many research studies. All of these relate to the precision of a single test conducted at one site on the animal whereas the precision that is important is the precision of the measured value as it represents the entire fleece. The precision of any value based on a calculation for one site will underestimate the precision relevant to the entire fleece, as it inevitably does not include the variation over the fleece. A model, which aims to represent the precision of the entire fleece, has been developed by Marler and Couchman (2001). Any estimate of precision will be dependent on the procedures used to determine the average value. As any change in the procedures is likely to have an impact the precision, quoting a 95% confidence limit without the detail procedures that accompany it is meaningless. It should be noted that in the wool industry, confidence limits are generally a statement of the capability of a documented IWTO Test Method or Australian/New Zealand Standard. No such Standards exist for OFDA2000 or FLEECESCAN. This means operators of both technologies can use whatever sampling and measurement regimes they decide is appropriate.

This report describes data from a series of trials conducted on one property. The 95% Confidence Limits relevant to three different measurement systems were determined:

• The OFDA 2000 measuring a single staple taken from one site on-farm;
• The LASERSCAN laboratory testing of a midside sample taken on-farm; and
• The minicore sampling of the skirted fleece and testing on a FLEECESCAN system in a store environment.

The 95% Confidence Limits relevant to the entire fleece were determined for the three different measurement systems and these were in turn compared to the precision of an IWTO Core Test as follows:

# Note the Between-Sheep Range of SDD and CVD for the OFDA2000 measured fleeces was lower than the Between-Sheep Ranges measured by FLEECESCAN and Laboratory LASERSCAN. N/A denotes Not Available.

These Confidence Limits are relevant to the sampling procedures and laboratory practices of the participating testers. The Confidence Limit will be widened if the number of measured fibres is less than that used in this study. Some FLEECESCAN operators are known to measure 600 fibres. This will result in a small increase in the reported Confidence Limits (i.e. ± 1.02µm to ± 1.04µm for MFD). Unlike the traditional midside sampling and Laboratory testing no Industry agreed Standards exist for either the OFDA2000 or FLEECESCAN. Hence, wool producers need to be aware that individual operators can determine their own sampling and testing procedures.

Citation

"A Comparison of the Performance of On-Farm OFDA2000 and In-Store FLEECESCAN - Part 1: The Precision of the Measured Fibre Characteristics of a Fleece", J.W. Marler,K.A. Hansford, I. McLachlan, Report CTF08, Commercial Technology Forum, IWTO Barcelona Meeting, May 2002