- In many wool-growing businesses, Staple Strength (SS) is an important profit driver affecting clean price. SS is heritable and good responses to direct selection have been shown over a reasonable number of years. However direct measures of SS on individual animals is expensive and for many years breeders have used Coefficient of Variation of Fibre Diameter (FDCV) as a proxy for direct measurement of SS, since FDCV is measured and reported automatically when Fibre Diameter is now measured. FDCV is genetically moderately strongly correlated with SS. This makes FDCV a useful indirect indicator of SS, without incurring the expense of measuring individual sheep directly for SS. In recent years, breeders have been measuring their sheep at earlier ages and in shorter wool. There have been questions raised regarding the effect Staple Length (SL) has on the accuracy of SS breeding values.
Is Fibre Diameter Variation Along the Staple a Good Indirect Selection Criterion for Staple Strength?The coefficient of variation of fibre diameter (CVFD) within the mid-side fleece sample is currently used to predict staple strength (SS) in Merino sheep (4.5 year old ewes). CVFD measures fibre diameter variation both between fibres and along wool fibres. It has been suggested that selection to improve staple strength should concentrate on reducing fibre diameter ariation along the staple, rather than CVFD. Our results indicate that measurements of fibre diameter variability along the staple had low heritabilities to moderate (0.01 to 0.20) and a low to moderate (0.15 to -0.43) phenotypic correlation with staple strength. In comparison, CVFD was highly heritable (0.78) and had a moderate (-0.44) phenotypic correlation with S. This suggests that there would be no advantage in using measures of fibre diameter variability along the staple as an indirect selection criterion for SS compared with the information provided by CVFD measured in a mid-side fleece sample.