OFFM technology trials

AWI conducted trials into the comparison of OFFM measurement against the Australian Wool Testing Authority methods and has drawn conclusions regarding accuracy and final recommendations for use.

AWI has released the results of a trial to compare on-farm and Australian Wool Testing Authority (AWTA) measurement of wool samples collected on farm.

The trial results have resolved the issues surrounding when and how the two competing machines, Sirolan FleecescanTM and OFDA2000, should be used and the bestlocation on a sheep for sampling.

The AWI-funded trial began in late 2002 and ran on 10 commercial wool growing properties across Australia, involving more that 3,500 sheep.

Conclusions

Definitions

Within the trial on-farm fibre measurement (OFFM) is defined as either:

  • On-farm sampling and measurement of fleeces using either OFDA2000 or Fleecescan instruments; or
  • On-farm sampling of fleeces and measurement of those samples in a AWTA laboratory.

Accuracy (Closeness to the 'true' result)

  1. For on-farm mean fibre diameter (MFD) measurements, OFDA2000 results measured on mid side samples and Fleecescan results measured on skirted fleeces gave equivalent accuracy compared with the 'true' fleece value.
  2. The pin bone as a sampling site does not give as accurate a measure for the 'true' fleece MFD as the mid side.
  3. When using OFFM to assist with clip preparation, it is unlikely that on-farm results from OFDA2000 mid-side and Fleecescan on the whole fleece will exactly match the certified core test results for lines created. Differences on individual lines of up to ±1 micron were observed.
  4. The finest lines will tend to be measure coarser than expected irrespective of the technology used for classing on MFD.
  5. The accuracy of measurement for the three other diameter parameters (Standard Deviation of Diameter, Coefficient of Variation of Fibre Diameter and Comfort Factor) as well as Mean Fibre Curvature was less than that found for MFD.

Precision (Repeatability of individual results)

  1. Mid side sampling and laboratory testing in accordance with standard AS/NZS 4492 gave the lowest (best) and equivalent precision (confidence limits of ±1.04 micron for Laserscan and ±1.05 micron for OFDA100).
  2. The Fleecescan (±1.17 micron) and OFDA2000 mid side sampling (±1.24 micron) were equivalent in precision.
  3. However, the effects of the above relatively small differences between the different measurement systems on sheep selection differentials were marginal.
  4. The pin bone sampling produced results which had higher (poorer) confidence limits (±1.39 micron) than mid side sampling.

General Recommendations

  1. To enable comparison across years for MFD, it is recommended that the same instrument/method is used.
  2. The use of Comfort Factor (CFR) in sheep selection, as it is relatively imprecise, is not recommended. CFR is closely correlated with MFD and consequently it is better to use MFD.
  3. Measurements on high value animals (such as rams) are likely to justify the use of higher precision testing (e.g. either the use of laboratory measurements or additional sampling and/or measurement on farm).
  4. For the commercial woolgrower selecting ewes, the benefits and convenience of on-farm testing may outweigh any loss in precision compared to laboratory measurement.  

Read the final report, chapter by chapter:

  1. Executive Summary and Background (PDF 202Kb)
  2. Trial Design and Phase 1 Trials (PDF 400Kb)
  3. Phase 2 Trials and References (PDF 199Kb)
  4. Appendix 8.1 Phase 1 Statistical Analyses (PDF 235Kb)
  5. Appendices 8.2-8.5 Phase2 Statistical Analyses (PDF 1.24Mb)
  6. Appendices 8.6-8.11 Statistical Background (PDF 191Kb)
  7. Appendices 8.12 and 8.13 Statistical Calculations (PDF 107Kb)
  8. Appendix 8.14 Original trial protocol (PDF 305Kb)

Resources

Contact

Geoff Lindon

Manager - Sheep Technologies
Tel: +61 2 8295 3100
Contact via email

 

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