The Impact of Test Result Precision on Genetic, Culling and Classing Decisions Taken on Farm

Abstract

The number of wool producers using On-Farm testing of Mean Fibre Diameter (MFD) has been increasing. Wool producers need to ask themselves the question as to why they are prepared to have tests performed on individual fleeces.

The most common applications are to gather information:

• for use in genetic improvement through a specific breeding program;
• for culling inferior animals;
• for use in classing the flock into lines of different Mean Fibre Diameters for sale; or
• for all of the above.

Each will have different outcomes in the interpretation of test data taken On-Farm or in-shed.

In the first two cases, it is the ranking of an individual sheep with respect to the other sheep in the mob that is the important parameter, whereas in the third case, it is important that fleeces are assigned to the correct line based on the measured MFD.

The precision, or more simply the repeatability, of the measurement will have an impact on all of the applications. For example, the more precise (i.e. a lower Confidence Limit) is the measured MFD the smaller the number of incorrect decisions that will be made. It is also important to appreciate that it is the precision of the estimate of the fleece that is important not the precision of the estimate at a single site such as the hipbone or the mid-side.

The impact of the precision of measurement on both sheep selection and fleece classing can be evaluated from a simple mathematical approach.

Citation

"The Impact of Test Result Precision on Genetic, Culling and Classing Decisions Taken on Farm", J.W. Marler and D.W. Crowe, Paper 37, Wool Industry Science & Technology Conference, October 2002, Hamilton, Victoria, Australia.