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 f leece sample is currently used to predict staple strength (SS) in Merino sh eep (4.5 year old ewes). CVFD measures fibre diameter variation both betwee n fibres and along wool fibres. It has been suggested that selection to imp rove staple strength should concentrate on reducing fibre diameter variatio n along the staple, rather than CVFD. Our results indicate that measurement s 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 co rrelation with staple strength. In comparison, CVFD was highly heritable (0 .78) and had a moderate (-0.44) phenotypic correlation with SS. This sugges ts that there would be no advantage in using measures of fibre diameter var iability along the staple as an indirect selection criterion for SS compare d with the information provided by CVFD measured in a mid-side fleece sampl e.