- 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.
Genetic Parameters and Relationships Between Fibre and Type Traits in Two Breeds of Peruvian AlpacasFour fibre traits (fibre diameter, FD; coefficient of variation of FD, comfort factor; and standard deviation of FD) were jointly analysed with six subjectively scored type traits (fleece density, crimp, lock structure, head, coverage, and balance) in two breeds of Peruvian Altiplano alpaca (Suri, SU; and Huacayo, HU) to ascertain their genetic relationship. A total of 2405 fibre records and 2194 type scores were available for the HU breed whereas these figures were 709 for fibre records and 650 for type scores for the SU breed. Estimated heritabilities for fibre traits were moderate to high, ranging from 0.565 to 0.699 in the SU breed and from 0.255 to 0.417 in the HU breed. Genetic and permanent environmental correlations between fibre related traits were extremely similar across breeds suggesting that these traits are fairly the same. Heritabilities estimated for the type traits tended to be lower than those estimated for the fibre traits particularly in the SU breed (ranging from 0.173 to 0.272). Fibre and type traits were, in general, genetically poorly correlated except for crimp in the HU breed, which had favourable correlations, from moderate to high, for fibre traits. In Altiplano areas in which fibre performance recording could not be implemented, crimp scoring makes it feasible to carry out mass selection in the Huacayo breed and furthermore include rural communities in national or regional selection programmes.
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.