Surface Scanning Electron Microscopy of Llama Fiber

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.