Section 3.3: Skin Biopsies

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Follicular Skin Biopsies

Note: Alpaca skin biopsies are currently performed primarily by Dr. Norm Evans, DVM and Ian Watt (Alpaca Consulting Services USA). Both gentlemen are highly regarded in our industry and have years of pointed experience in virtually all aspects of alpaca analysis, management, nutrition and husbandry. While technique and metric numbers and importance of certain metrics differ, both methods bring value to a breeder and both are highly recommended. While cost varies between $250 - $300 as of this writing (2010) many of us use our biopsy results to rate our alpacas and evaluate and make key breeding decisions with them.

A skin biopsy is a peek under the blanket to evaluate the fiber producing engine of our alpaca. This test is capable of getting much closer to revealing the genotype of the alpaca than the phenotype-driven histogram. Like the histogram sample, a skin biopsy is a sampling technique.

To perform a skin biopsy, a core of skin 10mm in diameter, roughly the size of a pencil’s eraser is extracted from a specific spot on the side of the alpaca. All the fiber is shaved from the spot and the sharp circular punch is lightly pressed into the skin and twisted. The sampling point will bleed, but dabbing it with a clean cloth will stop the bleeding quickly. A shot of lidocaine or equivalent can be administered to mask the pain and antiseptic can be administered and the sample point monitored for a few days for any sign of infection. It should be noted that the use of an anesthetic can swell the sample and so affect the reliability of the test results if injected intradermally but not if injected subcutaneously.

Quite a few breeders feel squeamish about having these tests done. It is not any more traumatic to the alpaca than having its teeth ground. And it gives critical results with regards to density and primary and secondary fiber statistics. Many of us would not think of purchasing a herdsire or even breeding to one without skin biopsy results.

The sample is put into a bottle of buffered formalin to preserve it and sent to a laboratory where it can be analyzed microscopically to produce several key statistics. These results are valuable tools for your alpaca breeding, buying and selling toolkit. The metrics include:

  • Accurate and meaningful density figures. Density is measured in follicles per square millimeter. There is a strong correlation between high density, uniformity and fineness. An alpaca can supply only so much of its energy into fiber production; relatively short thick fibers or longer fine fibers. If its skin happens to be densely packed with uniform follicles, the alpaca’s fibers will most probably be fine, the staples or locks well structured and uniform.
  • The ratio of secondary to primary fibers (S/P) tells us much about how many secondary fibers cluster next to the primary follicle. The higher this ratio, the more secondary fibers are present. This implies density, which implies fineness, uniformity, and so on.
  • Sebaceous glands are currently a contentious issue at this time and more research is needed. One theory says these glands do not create nourishment to fibers, they provide a wax and they take up growth area for follicle development i.e. large glands cause fibers to go around them and so can contribute to cross-fibering. Another gives high levels of importance to these glands as sources of nutrition and healthy fiber.
  • Neither secondary nor primary fiber medullation (air spaces within a fiber) can be seen with the naked eye. It takes a skin biopsy to reveal medullation albeit in a limited way.
  • The fiber clusters (primaries along with the secondary fibers) shape also implies density and uniformity.
  • The variation between the micron thickness of primary and secondary fiber populations can also give you a feel for potential handle – the lower the difference the more uniform, the better the handle. SD of primary and secondary fibers are a key indicator of uniformity.
  • Co-efficient of Variation of Fiber Diameter (CVFD) is an indicator of the fiber variation in diameter within the sample. CVFD is highly heritable and is negatively correlated with staple strength, so an alpaca with a high CVFD usually has a lower staple strength.
  • CV allows comparisons of like micron animals and nothing else – the ‘loss’ of staple strength is because of the fineness and not the CV per se. Furthermore, the biopsy report offers us a comparison between our own alpaca against any others that have been tested and the results published. This moves us from a purely subjective view - ribbons won visual inspection, etc, to an objective view - hard, measureable and comparable numbers.
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