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An introduction to evaluating alpaca fleece
attributes and interpreting alpaca fibre tests
Dr. Bruce McGregor,
Speciality Fibre Scientist,
Victorian Institute of Animal Science,
Department of Primary Industries, Attwood 3049.
McGregor, B.A. (2003). An introduction to evaluating alpaca fleece attributes and interpreting alpaca fibre tests. Alpacas
Australia, 40: 11-16.
Introduction
Assessing the attributes of alpaca fleeces subjectively by
eye is frequently very unreliable as alpaca fleeces show
large variations in quality attributes across the body. In
addition, our eyes are limited in their ability to discern
fibre diameter, the mean of other fibre attributes and the
extent of naturally occurring contaminants.
Alpaca fleeces are also affected by environmental
conditions, in particular humidity, but also by storage
conditions. The same limitations that affect alpaca fibre
apply equally to wool, mohair and cashmere.
To assist in the commercial trading of fibre for textile
processing, a range of testing procedures have been
developed to help reduce the errors associated with
subjective assessment. However, associated with objective
tests are a range of errors related to the sampling and
testing procedures. With objective testing it is possible to
quantify the likely extent of the errors associated with the
testing procedures employed.
To help breeders obtain reliable fleece test results the
starting point is understanding the types of variation found
in fleeces. This article discusses:
the sources and extent of variation within the alpaca
fleece;
the most appropriate method of sampling alpaca
fleeces; and
the application of this information for evaluating fibre
test results.
This article is based on research conducted with Australian
alpacas.
Variation within animal fleeces
The variation in the attributes within the fleece of animals
is related to the following components:
Within a staple.
Most of the variation in fibre diameter occurs between
fibres within a staple. The difference between the fibre
diameter of fibres growing from primary and secondary
skin follicles in an alpaca may be more than 20 µm. Many
medullated fibres in alpaca fleeces are more than 10 µm
coarser than the mean fibre diameter (McGregor 1999a).
Along the fibre.
Changes occur in the fibre diameter, dust, grease and
vegetable matter content as the fleece grows during the
year (McGregor 1999b). Nutritional changes, the affects of
disease and reproduction all influence fibre diameter along
the fibre.
Different positions within the fleece.
Fibre diameter, incidence of medullated fibres, grease, dust
and vegetable matter contaminants vary with the position
in the fleece (Aylan-Parker and McGregor 2002).
Differences between animals.
Within a herd of animals and between herds, animals,
especially from different properties, will differ in their
mean fibre diameter and level of grease and other
contaminants (McGregor 1999a, McGregor and Butler
2000).
Variation between components of the
fleece
Components of the alpaca fleece
The physical attributes of alpaca fleeces vary considerably
over the body. During the preparation of alpaca for sale,
the fleece is commonly divided into three components:
1. Saddle;
2. Neck;
3. Skirtings.
According to standard industry practice, the skirtings
consist of the fibre shorn from the belly, the top of the back
legs, the top of the front legs and apron (area between front
legs and neck) providing it is free of guard hair (Figure 1).
The site used for taking mid side samples, which is
discussed in the next section, is part of the saddle
component of the fleece (Figure 1).
Figure 1. Location of the saddle, neck and fleece components
that form the skirtings (front legs including apron, belly and
back legs) in alpacas and the site for mid side sampling.
Range in experimental animals
The range of measurements obtained from animals used in
this study varied as followed: age at shearing, 0.3 to 7.9
years; live weight at shearing, 30 to 110 kg; mean mid side
fibre diameter, 19.9 to 41.0 µm; fleece weight, 0.47 to 9.25
kg. These alpaca were typical of the Australian alpaca
herd.
Variation in fleece attributes
Australian alpaca fleeces show large differences between
the attributes of fibre from the mid side, saddle, neck, and
the remainder of the fleece (skirtings) and the mean for the
entire fleece (Tables 1 and 2, Aylan-Parker and McGregor
2002). The mean for the entire fleece was calculated to
include the skirtings and was calculated using the weight of
the fleece components.
Table 1. Variation in attributes of Alpaca fleece
measured from mid side samples and fleece
component grid samples including mean fibre
diameter (MFD) and coefficient of variation of MFD
(CVD).
Sampling site
MFD#
µm
CVD
%
Clean washing
yield %
Mid side site
27.5a
24.3a
90.2a
Saddle
28.8b
27.0b
91.4b
Neck
28.7b
28.6b
88.9a
Skirtings
37.6d
30.6d
92.8b
Mean entire fleece
31.2c
28.1c
# Within attributes, sampling site values with a different
superscript are significantly different.
Mean fibre diameter
In these alpacas there was significant variation in the mean
fibre diameter (MFD) over the body and this variation was
associated with high variation in the coefficient of
variation of the mean fibre diameter (CVD).
The fibre from the mid side site was 1.2 µm finer than fibre
from the saddle and neck, 3.7 µm finer than the mean for
the entire fleece and 10.1 µm finer than fibre from the
skirtings. Fibre from the saddle was 2.4 µm finer than the
mean for the entire fleece and 8.8 µm finer than fibre from
the skirtings.
There was a large variation in CVD over the body. The
CVD of mid side fibre was 2.7% lower than fibre from the
saddle, 3.8% lower than the mean for the entire fleece and
4.3% lower than for neck fibre.
Clean washing yield
The significantly lower clean washing yield of the mid side
and neck compared with that of the saddle and skirtings
shows that the distribution of dust, dirt and grease content
are not equally distributed over the body of alpacas.
Medullated fibre
The incidence of medullated fibres at the mid side site was
8.7% less than in the saddle, 10.8% less than the mean of
the entire fleece and 20.1% less than in the skirtings.
Similar differences were seen in the diameter of medullated
fibres (Table 2).
Table 2. Variation in medullated fibre attributes of
white Alpaca fleece measured from mid side samples
and fleece component grid samples.
Sampling site
Incidence by
number# %
Medullated fibre
diameter µm
Mid side site
24.4a
32.7a
Saddle
33.1b
34.4b
Skirtings
44.5d
41.1d
Mean entire fleece
35.2c
36.0c
# Within attributes, sampling site values with a different
superscript are significantly different.
In summary, for each fleece attribute, fibre at the mid side
site had lower values than the mean of fibre from the
saddle and the mean of the total fleece. For each fleece
attribute, except for clean washing yield, the saddle had
lower values than fibre from the pieces and the mean of the
total fleece.
Sampling methods
There are two main methods of fleece sampling available
for alpaca breeders: the mid side and the grid sampling
methods. Each method has it own advantages and
disadvantages.
Mid side sample method
Since 1947, the accepted method for testing sheep wool
has been to take a mid side sample (Turner et al. 1953).
The mid side sample has been used to test characteristics
of importance such as fibre diameter, fibre population,
staple length, density of fibres per unit area and staple
crimp.
In sheep, the theory behind using a mid side sample is that
a mid side sample test result is close to the mean of both
the top to underside and the front to rear variation found in
a fleece. For this to be true the mid side sample has to be
either mini-cored or testing after carding.
If a mid side sample is tested after butt cutting, as is
common in the United States of America, then this
assumption is not correct. A butt cut is a fibre sample taken
only at the end of the fibre closest to the skin. A butt cut
sample does not include any of the along the fibre variation
or differences due to position within the fleece.
Location of mid side sample
The site for taking the mid side sample in sheep is located
over the third last rib, halfway between the mid-line of the
belly and the mid-line of the back (Figure 1).
The mid side site is convenient to use for sampling because
it can be easily located during shearing and can even be
shorn without removing the entire fleece.
Problems with mid side sampling
In alpacas, if the mid side sample is taken to low, it may
include fibre that is really part of the pieces component. If
this happens the test results for mean fibre diameter and
other fibre attributes will be seriously over estimated.
The mid side sample mean fibre diameter has been
reported in Merinos and Alpacas to actually test finer than
the average for the whole fleece. In the study of the Merino
wool, this was particularly so for the finer sheep in the
population. It was suggested that in Merino sheep this was
due to intense selection over the years for finer fleece
based on the mid side sample rather than selection for a
finer entire fleece (Stadler and Gillies 1994).
While the mid side sample is highly correlated with the
mean fibre diameter of wool top (wool processed up to the
spinning stage), the mid side sample can be finer and the
differences may not be consistent (Fleet et al. 1993). This
suggests that the mid side sample may not be a reliable
predictive tool for the diameter of top.
Some of these differences may be due to the effect of fibre
breakage and subsequent loss during carding and noil
removal (combing).
Grid sample method
Grid sampling has been used for more than 20 years. The
grid sample includes differences due to position within the
fleece and so can detect variations in the fleece that the
mid side sample does not detect. For example, Butler et al.
(1991) found that processed wool top produced from
Merino wool was better predicted by grid sampling than by
mid side samples.
Grid sampling is the best method for taking samples from
cashmere goats as the mid side sample overestimates the
commercial yield of cashmere and underestimates
cashmere fibre diameter (McGregor 1994).
Method used for grid sampling
The grid sampling technique involves:
1. laying out the shorn fleece to be tested on a flat
surface, ideally on a table measuring about 3 m2. The
fleece needs to laid out evenly.
2. take 16 to 32 random grab samples from the surface of
entire fleece. To help this process it is common for
breeders to lay a physical grid over the fleece and to
take a sample from each grid. A suitable grid can be
made from plastic garden trellis mesh with a mesh size
of approximately 10 cm x 10 cm. The idea is to take
unbiased samples by pulling a tuft of sample from
each square in the grid.
Potential benefits of using grid sampling
Grid sampling can be completed while the next alpaca is
being shorn or can be undertaken after a fleece has been
stored.
Grid sampling avoids the problems found with core
sampling of entire fleeces. Core sampling is time
consuming but does include variation due to position
within the fleece. However core sampling cuts staples in
the fleece thus reducing the fibre length.
Sampling and testing variability
If repeat samples are taken from a fleece, differences in the
reported test measurement will usually be found. These
differences are related to two main causes.
Variation between samples
Each sample submitted for testing is different. These
differences are related to the variation in animal fleeces
discussed earlier but in this case are due to sampling
variation. Samples are also frequently sub-sampled once or
twice and variation also occurs during these processes.
Variation between tests
Variation occurs between tests. This variation can be
related to preparation of the sample and the operation of
the equipment. Each sample tested by the equipment is
different, so some differences in the reported measurement
are to be expected. Scientific test laboratories regularly
monitor their testing procedures to ensure the reliability of
the test results.
Interpreting test results
Alpaca growers need to be aware that each test has an
inherent error related to the variability associated with
sampling and testing procedures. This measurement error
exists even if only one sample is taken and measured.
Some growers have submitted fleece samples to different
fibre testing services and expressed criticism at the
“difference in results” they receive. Such an outcome is to
be expected. But do these “different results” really
differ?
Sampling variance in Australian alpaca
By determining the sampling variance, the 95 percent
confidence limits can be calculated for a particular
sampling and testing procedure. The sampling variance and
confidence limits for mid side and saddle grid samples has
been measured in Australian alpacas (Tables 3 and 4,
Aylan-Parker and McGregor 2002).
The sampling variance for the alpaca fibre mean diameter
attributes shown in Table 3 are similar to values reported
for Merino wool.
Table 3. Sampling variance for fibre attributes
measured from mid side or saddle grid samples in
Australian alpacas.
Attribute
Mid side
Saddle
Mean fibre diameter, µm
0.7
3.6
Mean fibre diameter CV, %
1.4
3.4
Incidence medullated fibre, % weight
8.3
95
Medullated fibre diameter, µm
1.1
3.8
Clean washing yield, %
4.4
6.0
Except for clean washing yield, the sampling variance for
saddle grid samples was generally 2 to 4 times greater than
the sampling variance for mid side samples. As a
consequence, for most fleece attributes, the 95%
confidence limits for the saddle grid sample were about
double those of mid side samples (Table 4).
Table 4. The 95% confidence limits for fibre attributes
measured from mid side or saddle grid samples in
Australian alpacas.
Attribute
Mid side
Saddle
Mean fibre diameter,
1.6
3.7
Mean fibre diameter CV
2.3
3.6
Incidence medullated fibres, % weight
5.7
19.1
Medullated fibre diameter
2.0
3.8
Clean washing yield
4.1
4.8
Sampling variance for the incidence of medullated fibres in
saddle grid samples was very high, possibly due to the
difficulty in sampling and measuring these fibres.
Contamination of saddle fleece samples with fibres from
the pieces and by coloured fibres will also increase the
sampling variance of medullated fibres.
Evaluating and undertaking alpaca fibre
testing
Use of mid side sample
The mid side sample was found to be an appropriate
sample from which to predict the mean fibre diameter and
the clean washing yield.
The mid side sample does not measure a large enough area
of the fleece to detect sufficient variation in mean fibre
diameter coefficient of variation (CVD) or in the incidence
of medullated fibres.
Use of the saddle grid sample
Breeders wishing to improve CVD and/or spinning
fineness (McGregor 1998) measurements of the alpaca
saddle, in the most efficient way, should use the saddle
grid sample, since the mid side sample is not as accurate
for use in the selection of stock for breeding programs.
Breeders using either mid side samples or saddle grid
samples to improve total fleece CVD, will improve neck
CVD at the same time with similar effectiveness.
The saddle grid sample was found to be the appropriate
sample to predict the incidence of medullated fibres in the
entire fleece.
Sampling procedure
The large 95% confidence limits for all the tested fibre
attributes indicate that alpaca breeders and advisers need to
consider taking suitable duplicate measurements and other
precautions during breeding and animal selling programs.
Using the confidence limits
The 95% confidence limits for mean fibre diameter (±
1.6 µm) show that alpaca breeders and advisers need to
exercise caution when interpreting absolute fibre test
results. This data indicates that breeders cannot
confidently distinguish between animal test results where
the mean fibre diameter differs by less than 1.6 µm. See
examples below.
There is only a 5% chance that two alpacas with
the following mid side test results are different:
a) 19.7 µm compared with 21.2 µm
b) 25.9 µm compared with 27.4 µm
Small differences in MFD are unlikely to be valid
grounds upon which to discriminate against animals.
This interpretation has even greater weight when using
saddle grid samples to select animals, as the sampling
variance for these samples is at least twice that of mid side
test results.
Differences between years and properties
It is not valid to compare the fibre testing results obtained
among properties or between years unless special
precautions are taken during the collection and analysis of
data. Large between year differences in the environment
will affect alpaca fibre attributes (McGregor 2002) and
property and year affects can interact (McGregor and
Butler 2000). Thus during the design of genetic
improvement programs, arrangements must be made to
account for these influences if serious attempts are to be
made at identifying real genetic differences.
Conclusions
If alpacas are to be selected for characteristics such as low
mean fibre diameter and high fleece weight then the mid
side sampling site is recommended.
If alpacas are to be selected for low mean fibre diameter
coefficient of variation, low incidence of medullated fibres
and other characteristics of medullated fibre, then the
saddle grid sampling technique is recommended.
Alpaca breeders and advisers need to exercise caution when
interpreting absolute fibre test results. Evaluation of fibre
attributes among alpacas should take into account the 95%
confidence limits of the sampling procedure.
Acknowledgments
The financial support of the Rural Industries Research and
Development Corporation and the Specialised Rural Industries
Program of the Department of Primary Industries (Victoria) is
gratefully acknowledged. Ms. J. Aylan-Parker, Ms. A. Howse
and Mr. C. Tuckwell are thanked for their assistance.
References and further reading
Aylan-Parker, J. and McGregor, B.A., 2002. Small Ruminant
Research, 44: 53–64.
Butler, K., Dolling, M., Marland, D.J., Naylor, G.R.S., Phillips,
D.G. and Veitch, C., 1991. In “Proceedings Fibre Diameter
Review Conference”, 54 pp. (CSIRO: Belmont, Victoria).
Fleet, M.R., Foulds, R.A. and Lampe, F.J., 1993. Wool
Technology and Sheep Breeding, 41: 307-316.
McGregor, B. A., 1994. Animal Production in Australia, 20:
186-189.
McGregor, B.A., 1998. Australia Alpacas, 23: 3-8.
McGregor, B.A., 1999a. In “Australian Alpaca Fibre : Improving
Productivity and Marketing” pp. 6 – 46. RIRDC Research Paper
Series No. 99/140. (RIRDC: Barton, ACT).
McGregor, B.A., 1999b. Proceedings Australian Alpaca Industry
Conference, Adelaide. pp. 88 –94. (Aust. Alpaca Assn.: Box
Hill, Victoria).
McGregor, B.A., 2002. Small Ruminant Research 44: 219–232.
McGregor, B.A. and Butler, K., 2000. Analysis of alpaca fibre
data and implications for fibre screening standards. Report for
The Australian Alpaca Association. pp. 18. (Department of
Natural Resources and Environment: Attwood).
Stadler, W. and Gillies, R.I., 1994. Wool Technology and Sheep
Breeding, 42: 319-326.
Turner, H.N., Hayman, R.H., Riches, J.H., Roberts, N.F. and
Wilson, L.T., 1953. Division of Animal Health and Production
Report No.4 (Series S.W.-2), 92 pp. (CSIRO: Melbourne).
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and its employees do not guarantee that the publication is without
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