- Variation in fibre diameter over fleece of Angora goats
|Last update: November 22, 2010 02:14:51 PM|
VARIATION IN FIBRE DIAMETER OVER THE FLEECE OF ANGORA GOATS
M. A. Snyman
Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900, South Africa
email: Gretha Snyman
Fibre diameter is of critical importance in determining the eventual textile qualities and final manufacturing applications of mohair. Fleece traits which contribute to the economic value of mohair, are fibre diameter, staple length, style and character and evenness of fleece. Of these, fibre diameter has the overriding influence on price, as is evident from the price difference between hair from kids, young goats, and fine and coarse adults. The importance of evenness of fleece lies therein that a much smaller proportion of the fleece would go into the neck or britches lines, and a larger proportion into the more expensive fleece lines.
During the past few years, objective measurement of fibre diameter has become an essential tool in selection of breeding animals, as well as in preparation of the clip; the Every Goat Tested (EGT) concept gaining in popularity over the past year or two. The aim with EGT is to minimize variation in fibre diameter within mohair bins, by classing fleeces with similar fibre diameter together. It is therefore important that classing should be based on fibre diameter obtained from a sampling site on the fleece, which has the highest correlation with overall fibre diameter of the entire fleece. The question is, which site on the fleece will be the most suitable for this purpose?
Fibre diameter was measured with the OFDA2000 on different parts of the fleece in 50 kids from the Grootfontein Angora goat flock, as well as in 50 kids and 145 ewes from the Jansenville fine hair experimental flock. Samples of kids were taken just prior to the second shearing of the kids, while samples of the ewes were taken prior to the shearing in July. Samples from the following sites on the fleece were analysed: midrib, hipbone, britch, shoulder, belly, neck and back. A single sub-sample (prepared from 3 different locks) was analysed for each goat for each site sampled. For each goat, fibre diameters obtained from the different sites were averaged to obtain overall fibre diameter of the fleece. Correlations were estimated among the different fibre diameters.
In the Grootfontein kids, fibre diameter varied from 27.9 µm at the hipbone to 31.8 µm at the neck - a range of 3.9 µm over the fleece. The lowest fibre diameter in the Jansenville kids was obtained for midrib samples (23.3µm), and the highest for neck samples (25.9µm) – a range of 2.6 µm. In the Jansenville ewes, fibre diameter varied from 31.2 µm for britch samples, to 34.4 µm for neck samples – a range of 3.2 µm. In the Grootfontein kids, CV of belly samples (26.5 %) was the lowest, while CV of the shoulder samples (25.6 %) was the lowest in the Jansenville kids. CV for hipbone samples was the highest in kids of both flocks. CV of belly samples (25.5 %) of the Jansenville ewes was the lowest, while CV of the shoulder and britch samples was the highest (28.9 %).
From the results it is obvious that fleeces of the Jansenville kids were more even than those of the Grootfontein kids. Evenness of fleece is one of the subjective fleece traits in Angora goats that vary a lot between different flocks and studs. This was also evident from a study done in the early 1990’s where goats from various breeders, as well as the Jansenville experimental flocks were assessed for different subjective fleece traits. Evenness of fleece was one of the traits which showed a lot of variation among animals, as well as among the different studs.
Correlations among fibre diameter at the different sites were all significant (P<0.0001), those of the neck with the other sites being the lowest. Fibre diameter of the midrib sample had the highest correlation with overall fibre diameter of the fleece in all three flocks measured, namely 0.95 in the Grootfontein kids, 0.93 in the Jansenville kids and 0.92 for the Jansenville ewes. Therefore the midrib could be regarded as the most suitable sampling site for the determination of fibre diameter.
From the results of this study it is evident that there is substantial variation in fibre diameter over the fleece of individual Angora goats. This would have an impact on classing of fleeces on the basis of fibre diameter determined on a specific site on the fleece into specific mohair bins. Fibre diameter of the midrib sample had the highest correlation with overall fibre diameter of the fleece and is therefore the most suitable sampling site for determination of fibre diameter. This is in accordance with work done earlier on sheep, where the midrib was also the most representative sampling site for fibre diameter. Furthermore, an effort should be made to select for animals with more even fleeces in terms of fibre diameter.