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Surface Scanning Electron Microscopy of Llama Fiber
© 2006 By Andy Tillman
SEM demonstrates that the cuticular cell length of
suri and single-coat llamas may identify them as a distinct
breed.
The Washington State Disease Diagnostic Lab (WADDL) in Pullman,
Washington analyzed 19 llama fiber samples with surface scanning
electron microscopy in February through November, 2005. The
WADDL normally uses scanning electron microscopy (SEM) to
identify virus and bacteria species for the State of Washington.
Samples were prepared by SEM instructor Dr. Chris Davitt,
PhD, who took two micrographs of each fiber sample.
All members of the Camel Family were analyzed with the exception
of the Dromedary camel. Beyond llamas, the study included
35 suri alpacas, eight huacaya alpacas, six vicuña,
five guanaco, and two de-haired Bactrian camels. As a reference,
other specialty fibers were tested, including white Angora
rabbit, washed mohair, Bombay silk, Soft Rolling Skin (SRS)
merino wool, and both domestic and imported cashmere.
SEM scanning demonstrates that the cuticular cell scale length
of suri and single-coat llama fiber is measurably different
from a short-wool double-coat llama. Cuticular scale length
is expressed as the Mean Scale Frequency (MSF) per 100 micron
(µ) field of view as measured by the SEM. High-luster
suri and single-coat llama fiber appear to be most similar
to suri alpaca and cashmere. This study has important implications
for the llama industry, as it strongly suggests that suri,
and even single-coat llamas, are a distinct breed from a double-coat
ccarra-type llama. Due to its very low cuticular scale height,
llama breeders can now objectively explain why their products
have superior handle, compared to wool of similar average
fiber diameter (AFD).
Research on cashmere and mohair has demonstrated that a low
MSF is highly correlated to luster. “Luster is strongly
associated with mohair, based on its relatively large surface
cuticle scales and low cuticle scale edge height relative
to merino wool,” according to Bruce McGregor in Australian
Farm Journal. In other words, the longer cuticle scales reflect
more light than a series of shorter scales.
SAMPLE DEMOGRAPHICS
Twelve suri, six single-coat, and one short-wool llamas were
analyzed. Ten subjects were male and nine female. Samples
were collected from virgin fleece at 9–13 months of
age. Three samples were collected from shorn fleeces and the
remainder from unshorn llamas in the same location used by
Yocum McColl for laser scanning.
A “single-coat” fleece does not have to be de-haired
prior to processing. A “double-coat” must be de-haired.
Angora rabbits are single-coat, while cashmere and mohair
goats are double-coat. A goat fleece can have up to 75 percent
guard hair, and for this reason Chinese cashmere is combed
rather than shorn. Llamas are somewhere in between these two
extremes. As used in this article, a single-coat fleece has
little or no visible guard hair that could be de-haired by
hand.
The 18 suri or single-coat llamas that were analyzed had
a mean AFD of just 21.1 µ with less than 9.2 percent
coarse fibers (>30 µ), with a range of 19.9 - 24.6
µ and 5.4 - 11.7 percent coarse fibers. The single “double-coat”
llama was a classic short wool with 24 µ under-coat
and >50% coarse fibers. Its AFD was 32 µ. We did
not test more ccarra-type llamas due to the high cost of SEM.
(Typical industrial application of SEM costs about $300-400
per micrograph). A literature search of specialty fibers revealed
that ccarra-type llamas have a MSF of 11-12 scales/100 µ1,
so no further analysis was made.
WHY SEM?
The SEM micrographs provide detail not obtainable with a
conventional compound microscope. An optical microscope uses
visible light of a wavelength of several thousand angstroms
(Å). Such an instrument is actually a photon microscope,
since a ray of light is a beam of photons. An electron microscope
uses a beam of electrons instead of a beam of light.
The main advantage of the EM microscope is its potential
for very high resolving power. This is based on the possibility
of using electrons whose de Broglie wavelengths are less than
1Å. Objects as small as 2.3Å have been resolved,
a feat forever beyond the capability of a microscope using
visible light.
It is possible to count cuticle scales on the surface of
a fiber sample with an optical microscope, but to do so requires
coating the fiber with lacquer to provide contrast. Unfortunately,
the lacquer greatly exaggerates the height of the scale. For
this reason, SEM is probably the most appropriate method of
analyzing South American Camelid (SAC) fiber. However, use
of the optical microscope can reveal to what extent the fiber
is medullated.
TRANSMISSION ELECTRON MICROSCOPY (TEM)
Suri is even more different from double-coat llama fiber
than SEM indicates. The cortex or center of suri fiber is
probably comprised of a single cell type. Wool and huacaya
fibers have two distinctly different cell types, (orthocortical
and paracortical), which is responsible for the fiber having
crimp. While SEM examines the surface structure of a fiber,
TEM can be used to visualize the cortex of a single fiber
viewed on end. The fiber is cut in two and the TEM, which
can visualize an area as small as 2µ, takes a digital
picture of the fibers cortex. Optical analysis of suri fiber
suggests it has a single (paracortical) cell type, and this
would help explain why it is such a straight fiber. It is
much more time consuming to prepare samples for TEM than SEM,
and therefore more expensive. TEM of llama fiber will probably
require industry support.
RESEARCH PROTOCOL
Micrographs were taken at an accelerating voltage of 15–20
Kilo Volts (KV) and 1,000X. The quality of the micrographs
taken by a skilled EM instructor like Dr. Davitt made it possible
to accurately measure the length of each scale on a fiber,
the height of scale, frequency of scale, angle of scale, and
fiber diameter. For the purposes of this article, the relatively
simple International Wool Textile Organization (IWTO) DTM-XX-97
methodology was used with the exception of viewing the samples
at 1,000X magnification rather than 600X. The higher magnification
was necessary to accurately measure alpaca and llama scale
height, which is almost impossible to measure even with digital
imaging tools. Wool has a scale height of 4–8 micron
and can easily be measured at 600X. Measuring scale height
is important, since scale height is one reason alpaca and
llama fiber has a low coefficient of friction and may feel
much finer than it is.
Following IWTO DTM-XX-97 methodology, the author counted
the number of cuticular scales in a 100 µ field of view.
Scale frequency is expressed as a Mean Scale Frequency (MSF).
A lower MSF indicates a longer cuticular scale. A higher MSF
indicates a series of shorter scales. A literature search
revealed that a MSF for wool ranges from 10–12, depending
on breed, 6–8 for de-haired cashmere, and 6–7
for de-haired mohair.
OPTICAL ANALYSIS
Dr. Davitt supplied me with 1.7 megabyte, 8-bit gray scale,
TIFF files captured with a Scion Grabber card from the SEM.
Two micrographs were taken of each sample. One to three fibers
could be measured in each micrograph. These black and white
micrographs had remarkable brightness and contrast. I used
the National Institute for Health (NIH) Image-J software to
measure the diameter of the fiber, the length of each scale,
and using the angle tool, the angle of scale perpendicular
to the fiber. Measuring the length of each scale with the
NIH software is much more time consuming than using the relatively
simple IWTO methodology, but does provide a larger data base.
While llama breeders are struggling to find a definition
of suri that is comprehensible to neophytes, show superintendents,
competitors and judges, the IWTO and Italy’s Supreme
Project1 have gone a long way toward doing so already.
“7.0 Scale/100 micron seems to be a distinctive
parameter for suri.”1
Most of the suri llamas in our study would qualify as suri
even under this demanding international textile standard.
However, MSF should not be disassociated with scale height.
When the scale height is impossible to measure, and you have
to zoom in on the micrograph to 200 percent actual size to
even visualize a scale edge, you have what is essentially
a mono-filament like silk. Several of the suri llamas and
alpacas with a relatively high MSF were so smooth that it
still had a very slick, cool handle.
CCARRA LLAMA
The surface structure of a ccarra fiber sample looked almost
identical to huacaya alpacas and guanacos. This short-wool
llama had a MSF of 11.5. Secondary fibers averaged 24 µ
but looked very “sheepy.” Their primary hair follicles
(guard hair) had a much greater AFD, and was routinely >50
micron.
The guard hair had a MSF of 16.5 with a range of 14-19. The
surface structure of a double-coat llama shows a much greater
similarity to huacaya fibers than suri. This may be of interest
to archaeozoologists and could have some taxonomic significance.
Reducing the percentage of guard hair from llama fleece has
probably been the single most significant achievement for
llama producers in the last 30 years. The high percentage
of guard hair in South American fleeces is the main reason
why llama fiber has failed commercially. The Aymara Development
Council has recently opened a dehairing facility in Bolivia,
and this has already increased demand for llama fiber.
SINGLE-COAT LLAMA
Secondary fibers of single-coat llama were very suri-like
with a MSF of 8.0 and a range of 7.5 - 10.0. These highly-evolved
llama fleeces are indicative of what is shown in Alpaca and
Llama Show Association (ALSA) medium and long-wool halter
classes. Starting from very humble beginnings, it has taken
llama breeders 30 years (10 generations) to evolve from a
double-coat to a single-coat fleece. These llamas had a scale
height less than or equal to huacaya alpacas. Handle could
be either warm or cool depending on scale height, crimp, and
percentage of guard hair. Basically, if a fleece exhibits
natural luster, it will have a low MSF. If it has a “cool,”
slick handle, it will have a lower MSF than a dull or chalky
fleece.
SURI LLAMA
The suri llama samples had a MSF of 7.0, an average of 7.4,
and a range of 4–11. To appreciate how exceptional this
is, remember that a MSF of 7.0 is slightly superior to Antonini’s
study of Peruvian suri alpacas!1 This suggests that the Argentine
wool-grading classification known as “Lustre,”
which blends any SAC fiber with a low MSF together, while
certainly controversial, may be justified. There did not appear
to be a correlation between a low MSF and AFD. This is good
news to llama breeders since it should be possible to simultaneously
reduce AFD while increasing luster.
SUMMARY
SEM has determined that suri and single-coat llamas are probably
a distinct breed of llama and are measurably different in
both MSF and scale height than guanacos, huacaya alpacas and
double-coat llamas. SEM makes a convincing case for maintaining
a separate registry for suri and single-coat llamas. Dividing
llamas which have been selectively bred for enhanced fiber
characteristics into their own show divisions can certainly
be justified. Our show associations, registries and judges
should keep abreast of fiber research which is rapidly advancing
the knowledge of camelid fiber characteristics. Progressive
llama breeders can rightfully claim to produce a fleece which
has an MSF and luster which is similar to cashmere with an
AFD much less than mohair.
- SUPREME-Project: Cuticular Cell Mean Scale frequency in
Different Types of Domestic South American Camelids (SAC);
M. Antonini et al. University di Camerino Press, Italy,
(1996).
Andy and Dr. Cheryl Tillman funded this research on
alpaca and llama fiber. The Tillmans imported the influential
colored suri alpacas and llamas from Hacienda Acero Marka
near La Paz, Bolivia in 1996. Andy has raised llamas since
1975 and alpacas since 1982. He is a member of the SLA board
of directors and The Suri Network research committee. Cheryl
Tillman has been a camelid veterinarian since 1985. She
sits on the board of directors for the US Animal Health
Association, serves on the AOBA/ARI Government & Industry
Relationship committee, and has reviewed research proposals
for Morris Animal Foundation for many years. They can be
contacted at andy@tillmansranch.com.
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