Genetics and Breeding

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. more »

Fibre diameter, fibre length, and the ratio of fibre length growth to mean fibre diameter (L/D), fibre diameter profile characteristics, and staple strength were examined in 16 fine wool Merino wethers in a 12-month field experiment. Variations in fibre diameter, fibre length, and L/D were shown to be associated with fibre diameter profile characteristics and staple strength. At constant fibre diameter, L/D was significantly positively related to variation in fibre diameter along the staple. A positive correlation between seasonal variation in L/D and variation in diameter between fibres was also observed. Staple length was significantly positively correlated with along-staple variation in fibre diameter and negatively correlated with variation in fibre diameter among fibres. Among-fibre variation in fibre diameter was not significantly correlated with along-staple variation in fibre diameter. Seasonal variation in fibre length growth, fibre diameter, and the ratio of length to diameter throughout the year was associated with increased variation in fibre diameter along the fibre diameter profile and reduced staple strength in grazing sheep. Seasonal variation in fibre diameter was mostly related to mean fibre diameter, L/D, and seasonal variation in fibre length growth rate. Changes in fibre diameter throughout the year were also related to seasonal changes in body weight, fat depth, and skin thickness. more »