Last update: November 22, 2010 02:25:12 PM E-mail Print

 

Variation in fibre diameter over the fleece of Angora goats and the most suitable

sampling site for determination of fibre diameter with the OFDA2000

 

Dr. Gretha Snyman, Andries Strauss


Grootfontein Agricultural Development Institute, P/Bag X529, Middelburg (EC), 5900
email: Gretha Snyman

 


Fibre diameter is of critical importance in determining the eventual textile qualities and final manufacturing applications of mohair. Considering the decline in world mohair production, and the large proportion produced in South Africa (62% of the world mohair production), it is essential that the quality of the clip, especially in terms of fineness, be maintained. 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. Staple length and then style and character, have the largest influence on price of mohair with the same fibre diameter (Hunter, 1993). During the classing process, the neck and britches are removed and classed separately, because of differences in the fibre diameter and length from the rest of the fleece (Van der Westhuizen et al., 1988). Lower prices are also obtained for these lines. 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?
 
Various methods are available for the objective measurement of fibre diameter. Most of these, however, are rather expensive, time consuming and laborious and need to be done in a laboratory after washing and preparation of the greasy mohair sample. The OFDA2000 was developed to be a portable instrument capable of real-time measurements of the fibre properties of greasy fibre with minimal sample preparation as an aid to selection or clip classing (Brims et al., 1999). It is therefore ideally suited for the application of EGT in practice. 
 
The OFDA2000 was used to determine the variation in fibre diameter over the fleece of Angora goats, and to determine which sampling site has the highest correlation with overall fibre diameter of the fleece, as well as of the mohair bin.
 
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 (employing the most suitable sampling and handling procedures as determined previously): 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.
 
Mean fibre diameter and coefficient of variation (CV) of fibre diameter obtained for the different sites over the fleece are summarised in Table 1 for the Grootfontein kids, the Jansenville kids and the Jansenville ewes. 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 Table 1 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. In order to minimize variation in fibre diameter within a mohair bin, it is important that fibre diameter of the sampling site should have the highest CORRELATION with overall fibre diameter, and not necessarily the nearest physical value than overall fibre diameter. Therefore the midrib could be regarded as the most suitable sampling site for the determination of fibre diameter.
In addition to the above study, samples were also taken at the midrib from 1200 kids, 800 young goats and 2000 ewes from a producer who makes use of the “Every goat tested” concept to class his mohair clip. All samples were analysed with the OFDA2000. Fleeces were classed in the different bales according to midrib fibre diameter. A list of animals which fleeces went into which bale was available. Subsequently, core sample fibre diameter was done on each mohair bin. Classing of fleeces into specific mohair bins based on midrib sample fibre diameter yielded satisfactory results. The correlations of individual midrib fibre diameter of fleeces with core sample fibre diameter were 0.93 for ewes, 0.96 for young goats and 0.97 for kids respectively.
 
Table 1. Mean fibre diameter and CV of different sites over the fleece of the Grootfontein kids, Jansenville kids and Jansenville ewes

Site

Grootfontein kids

Jansenville kids

Jansenville ewes

Fibre diameter (µm)

Coeff. of variation (%)

Fibre diameter (µm)

Coeff. of variation (%)

Fibre diameter (µm)

Coeff. of variation (%)

Midrib

28.5±2.5

28.3±4.5

23.3±1.8

26.1±3.1

33.1±4.2

27.3±4.1

Hipbone

27.9±2.4

29.5±4.8

23.7±1.9

27.4±4.2

31.7±3.7

27.4±3.7

Britch

30.6±2.9

29.4±4.8

23.3±1.9

26.5±3.1

31.2±3.7

28.9±4.4

Shoulder

28.9±2.4

29.1±4.3

23.8±1.6

25.6±2.9

31.8±4.3

28.9±3.9

Belly

29.9±2.9

26.5±4.5

23.9±1.6

25.8±3.2

34.3±4.3

25.5±4.4

Neck

31.8±2.9

27.4±3.8

25.9±2.4

27.3±3.4

34.4±4.5

28.1±3.9

Back

29.0±2.7

27.7±4.1

24.0±2.2

27.3±2.7

32.0±3.7

28.7±3.8

Overall mean

29.5±2.4

28.3±3.9

24.0±1.7

26.6±2.3

32.6±3.5

27.8±3.4

 
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.