Why Use an Alpaca Skin Biopsy?
-My arm is not a scale; my eye is not a microscope
Many of us spend a healthy amount of time evaluating our alpacas’ value. Many of our concerns deal with breeding strategies. We agonize over terms like ‘zipper crimp versus French fry crimp,’ ‘lock structure ’and‘ degrees of luster’. We cart our alpacas around the country and compete in halter and fleece shows, hoping to learn more as to the worth of our animals as measured against others. Whether we return home with a fist full of ribbons or empty handed, we may still puzzle over the questions like ‘which alpaca studs should you breed your best dam to?’ or ‘am I truly improving my herd with my breeding strategies?’ Even if we take the championship at a show, how do we know this title holder will produce improved offspring?
A big part of these concerns stem from the fact that halter and fleece judging offers a somewhat subjective (qualitative) view of what we can see. Additional key information can be revealed by an objective (quantitative) view; what we can measure. Histograms are testing staples (pun intended) for our industry. It is difficult to sell an alpaca these days without presenting a histogram to a prospective customer. We talk about average fiber diameter, standard deviation and curvature. But even these are external measurements. For more information on determining the true breeding worth of both our males and females, we need to peek under the blanket (pun intended), and look under the hood. This is why skin biopsy results are becoming increasingly popular as breeding, buying and selling tools – they offer great objective insight into what lies under the skin. A skin biopsy can get much closer to the genotype of the alpaca than the phenotype-driven histogram, which is in reality only a snapshot of a few alpaca fibers taken at one spot on a single day.
To perform a alpaca skin biopsy, a core sample, roughly the size of a pencil’s eraser is taken from the side of the alpaca. The sample is then 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:
- Density score
- Secondary to Primary fiber ratio which really determines how a alpaca fleece feels against the hand
- Sebaceous gland presence and density
- Secondary fiber medullation
- Fiber cluster shape and symmetry
- Micro variation between primary and secondary fibers
The alpaca is a two coated animal, like the Vicuna, Cashmere goats, and many other mammals. Nature protects these animals with a coat of thick primary hair-like follicles and a thinner, softer follicle. The thicker follicles, called primary follicles seem to act like support for the finer, secondary follicles. If the primary fibers are overly thick, we call them guard hair. These are the nemesis of the ‘prickle effect’ and ruin much of the soft handle of alpaca blankets and finished products. We breeders who are actively breeding for fineness and uniformity aim to breed thick guard hair out of our alpaca blankets and even reduce the size of the primary and secondary follicles; all in the name of handle. And handle, to me, along with the durability, ‘greenness’ and natural colors are the true magic of alpaca fiber.
The underlying makeup of an alpaca’s protective coat consists one primary fiber with a set of secondary fibers growing next to (not encircling) the primary follicle. Logic and supporting measurement tell us that the thinner we can make the alpaca’s primary fibers through selective breeding and the greater the number of fine secondary fibers the alpaca can produce, the finer, more dense and more uniform the alpaca blanket will be. This is the goal of many alpaca breeders, for the highest profits from our sheering harvests will come from remarkable softness coupled with a healthy quantity of sheared fiber. This is where an alpaca skin biopsy become critical.
- An alpaca skin biopsy gives us density figures. Density is measured in follicles per square millimeter. There is a strong relationship between high density and fineness. An alpaca can supply only so much of its energy into fiber production. If its fleece happens to be densely packed with follicles, the alpaca’s fibers will most probably be fine, the staples and locks will be well structured and uniform.
- The ratio of secondary to primary fibers (S/P) tells us much about how many secondary fibers sit next to the primary follicle. The higher this ratio, the more secondary fibers are present in the alpacas fleece. This implies density, which implies fineness, uniformity, and so on.
- Sebaceous glands provide nutrition and repair support to the follicles. The more glands there are, the more regular their shape, the healthier and brighter or more lustrous the fibers tend to be.
- Secondary fiber medullation (note that medullation (air spaces within a fiber) cannot be seen. It takes a skin biopsy to reveal these.
- The fiber cluster (primaries along with the secondary fibers) shape also implies density and uniformity.
- The variation between the micron thickness of primary and secondary alpaca fibers can also give you a feel for handle – the lower the variation the more uniform, the better the handle.
- Co-efficient of Variation of Fiber Diameter (CVFD) is an indicator of the between 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.
So how can the results of an alpaca skin biopsy help a breeder? The alpaca 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. Benchmark studies have been done and numbers are available to determine elite density, S/P rations and so on. We can begin to correlate those super alpaca studs that win in the ring against the also rans and also track these alpaca studs and alpaca dams for performance capabilities and for herd improvement through their progeny. And we are seeing that our halter and fleece judges are indeed selecting the best of the best in most cases, for there is a high correlation between judges’ choices of champions and the densest of alpacas. Whether these champions pass this on to their offspring though, is another matter. Progeny skin biopsy testing must be done.
Alpaca Skin Biopsy – Benchmarking Density Testing:
Per Dr. Evans,
‘Based on about 1800 biopsies, the average density in follicles per square millimeter for huacaya alpacas are about 39.75. The average S/P ratio is 8.75/1. For 270 Suri alpacas, the average density is 38.75 follicles sq mm. The average S/P ratio is 8.1. Superior breeding stock that seem to win in the show ring is 55-60+ and an S/P ratio of 10/1 will show better bundle structure in the show ring.’
‘Fiber cluster shape, symmetry, structure, or infrastructure is highly genetic but can be destroyed by sickness or infection. Ideally, we want all clusters to have an even distribution of fibers. Clusters that uniformly have 10 to 12 fibers are preferable to having one bundle with15 fibers beside a bundle with 8 fibers and another bundle with 11 fibers. This irregularity on the inside does not give the judges a good perception because of the irregularity on the outside. The fact is we can predict this before you ever select your breeding. Look for tight symmetrical clusters of the same size and shape on your biopsy rather than irregularly shaped clusters with uneven fiber numbers.’
‘Most all opinions agree that it is highly desirable to breed toward primary and secondary fibers that are healthy and near equal in size as measured in microns. The primary fibers (guard hairs) are usually straight, much larger, and have a prickle factor that is unpleasant to human skin. Our goal is to breed in the direction that both fibers are acceptable in size and as near equal in size as possible. Micron size appears strongly genetic but can be altered by sickness, weather extremes, nutrition, and other factors. The average variation that I see to date is 7.9 microns and anything under 5 to 5.5 microns seems very desirable and genetically strong.’
In summary: a density of 55-60+ follicles per square millimeter is elite. An S/P ratio of 10/1 is elite. These are the level of numbers needed to produce dense and fine alpacas.
Per Ian Watt:
How to get an alpaca skin biopsy done
There are two basic methods of testing. The Australian method, as tested by Alpaca Consulting of America (Ian Watt) and Dr. Norm Evan’s method. Each method has bench marked findings based on numerous tests. (Appropriate contact info will follow here).
A comparative analysis:
SafeHouse Farm Alpacas has gone through the expense of having two of our top herdsires alpacas tested by both Dr. Evans and Ian Watt. While the testing methods and results are different, using the same method for you animals is required it provide you with the same baseline in which to compare alpaca skin biopsy results.