Section 3.6: All About Biopsies

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B. Available Skin Biopsy Testing

There are two significant and accepted methods of testing currently available to us: (note: see appendices 2 for skin biopsies report examples.

1. Alpaca Consulting Services USA

Per Ian Watt:

The following definitions are designed to give a better understanding of both the details of a skin biopsy report and a means by which to utilize the information in making better informed, and more meaningful, selection and breeding decisions.

a) Mean Fiber Diameter (MFD):

The mean fiber diameter in a skin sample represents the diameter at a particular point of time – it is a “snapshot” of the fiber diameters at the time of skin sampling.

Prevailing environmental conditions, nutrition and general health and condition of the alpaca at sampling will affect the diameter of these fiber measurements.

In some alpacas the fiber follicles sit at an angle to the skin and therefore appear as oval shaped in the skin cross-sections. Suri appear to feature this particular trait more than Huacaya and in Huacaya, this trait tends to follow less dense counts.

To counter this structural formation, these fibers are measured across the smallest axis.

b) Co-efficient of Variation of Fiber Diameter (CVFD):

The CV of fiber diameter in skin samples is an indicator of the between fiber variation in diameter within the sample.

The CVFD accounts for about 80% of the total diameter variation (that is both between and along fiber, variation) in most cases.

CVFD is highly heritable and is negatively correlated with staple strength, so an alpaca with a high CVFD usually has a lower staple strength.

c) Secondary: Primary Ratio (S: P):

The ratio of secondary to primary follicles is correlated with density – generally, the higher the ratio, the greater the follicle density of that animal.

Note: with regards to derived secondary fibers. These are fibers that grow as part of the secondary fibers. These fibers come out at the top of the secondary follicle sheath as they grow and begin their emergence somewhere along the secondary follicle’s length. When slicing the slide material the biopsy procedure includes entering the sample’s epidermis and exposing all of the derived secondaries - that is, we see one hair for each follicle sheath, and, as we know that each follicle grows only one fiber and that each of those derived follicles have their own, albeit a short, sheath, we can identify them easily. What we can't do as yet is label derived and secondary hairs per se.

d) DP: Ds Ratio (DP: Ds):

The DP: Ds ratio indicates the relative size of the two fiber (primary and secondary) populations. It is calculated as the mean fiber diameter of the primaries divided by the mean fiber diameter of the secondaries.

Primary follicles are generally larger in diameter than secondaries so the ratio is usually greater than 1.0. For an alpaca where the primaries are substantially larger than the secondaries, the ratio will be much larger, for example, 3.0.

For an alpaca where the variation is not great, the ratio will be closer to 1.0.

It is possible to have an animal where the primary fibers are finer than the secondaries, which indicate a more homogenous fiber population and a ratio of less than 1.0.

Generally speaking, the closer to 1.0, the better the uniformity between primary and secondary fibers and the finer the fleece. This ratio then becomes an important selection point of difference between animals under consideration for inclusion into a breeding program.

e) Follicle Density:

This is probably the major characteristic because it governs the diameter of fibers and thus the total fleece weight.

The higher the density of follicles in the skin, the lower the diameter and the higher the fleece weight, assuming staple length is conserved.

Two significant errors arise in its measurement however:

The skin biopsies shrink during fixation and processing for measurement. This is corrected for, on the assumption that a 1cm biopsy was taken from un-stretched skin at the time of collection or sampling, and

Samples from young animals always have higher densities than they ultimately will end up with as mature alpacas. The expansion of skin (which causes a lowering of density counts) increases with age and body condition and musty be borne in mind when comparing alpacas of differing ages and sizes.

The OFDA 2000 Report.

When appropriate, an OFDA 2000 test will be done on the fleece sample snipped from the biopsy site as an addendum to the skin sample report.

When data is available, average daily growth rates for the staple is calculated and the crimp/cm (in Huacaya) is also counted.

A new measurement called “stretch percentage” is provided to indicate the amplitude of the crimp in the staple (not relevant in Suri).

A low stretch (under 10%) indicates a shallow amplitude, between 10 and 15% indicates a moderate amplitude and a stretch of over 15% indicates deep amplitude and is usually associated with moderate crimp/cm counts.

When talking about staple length, it is very important to establish whether the measurements being talked about are relaxed or stretched as two animals may have identical staple lengths but, when stretched, they vary by as much as 15 to 20% which reflects greater fleece weight from the same density.

2. Dr. Norm Evans, DVM Skin Biopsy Report

Per Dr. Evans,

Some breeders have requested information on how to use the results of fiber biopsies. The results of your biopsies, when coupled with the histogram, should give good direction to your breeding program if you wish to follow it.

The useful tools you get are 1) Density, 2) Secondary to primary ratio, 3) Sebaceous gland presence and density, 4) Secondary fiber medullation, and 5) Fiber cluster shape, symmetry, or infrastructure, and 6) Micron variation of the secondary and primary fibers.

1) Density is the number of follicles per square mm of skin. Based on about 2100 biopsies, the average for huacayas is about 40.25. About 300 Suris have averaged 39.5 follicles per sq mm. Superior breeding stock that seem to win in the show ring is 55-60+.

 2) The secondary to primary ratio is the number of smaller micron desirable fibers to each primary fiber or guard hair in each fiber cluster. The average that I have seen on about 1800 huacayas is about 8.75 to 1. The average S/P on about 300 Suris is 8.75 to 1. It seems that near 10 to 1 is desirable for the perception of better fiber cluster in the show ring. I count 25 fiber clusters and average than number for the S/P average so it may not agree with the picture scan. While it does make sense that a larger S/P ratio of maybe 15 to 1 correlates to greater density, a large percentage of the most dense biopsies that I have evaluated have S/P rations of 9 to 11 to 1 but with minimal connective tissue between fiber clusters. In going back 3 or 4 generations, I find the amount of connective tissue between fiber clusters seems to surface as a female trait which is passed on to the offspring whether male or female.

3) The sebaceous gland presence has not been mentioned until 2006. I have followed the progress of alpacas on fiber nutrients in my research for the past 5 years. I saw that some responded more rapidly than others. After the biopsies, I see that it is the ones with gland presence that responded better. After evaluating family lines, I see that these glands are appearing to be highly genetic. These glands provide a nutrition pathway to the fiber and are a very strong factor responsible for brightness and luster. When several judges started using this approach, looking for well nourished fleeces, I saw that I was headed in the right direction.

4) Secondary fiber medullation was thought to be bad. In fact, some say that all alpacas with secondary medullated fibers should be eliminated from the gene pool. The fact is that would take 98% of the Huacayas and Suris from the United States gene pool. The average that I see on biopsy is about 40-50% secondary medullation. The judges are actually rewarding it in the ring because higher secondary medullation relates to more defined cluster structure which gives the fibers the perception of strength and form. The lower the number of secondary medulated fibers, the better the handle.

5) 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 9 to 11 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. Secondary fiber medullation is appearing to be a strongly passed prepotent male trait. I see several males at 3 years of age with secondary fibers that average 19 microns and primary microns that average 32 microns. In most cases, their offspring show the same wide variation. A male with secondary fibers that average 22 microns and primary fibers that average 27 microns is much more desirable in my mind at this time as far as passing desirable prepotent genetic traits regardless of the S/P ratio.

6) Micron size and variation of the secondary and primary fibers gets a lot of press. 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. The 250 X scan of your biopsy gives a good indication of the micron variation on your particular alpaca. I count and measure 100 secondary and 50 primary fibers (depending on the specimen density) and show a typical view on this scan. This calibration is usually rather close to the histogram results where many more fibers are evaluated. Both are to be used as tools in selecting breedings. 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 any thing under 5 to 5.5 microns seems very desirable and genetically strong.

How do we use this info? You breed strong points to weak points in your selection process. To excel as a herd, some animals will simply not help to strengthen the gene pool. This is the reason for knowing the stats on the females as well as the males, if you really want to more rapidly potentate your genetics. In about 30% of the cases, where both females and males are biopsied, the females actually have superior genetic characteristics to the males that they are bred to. Every farm that I visit seems impressed with how their crias are improved compared to previous years. This certainly is the case and we notice that the show ring is becoming much more competitive. Much of this success can be a compliment to breeder management in the selection of males utilized as well as to improved nutrition. Close observation of the programs enjoying much success have utilized the above tools in breeding selection.

The goal of the industry is to produce the ‘finest fibered geldings in the world.’ I deal with 9-10 year old females that were 19 microns at 2-3 years of age, have had 6-7 crias, and are still at 19-20 microns. There are few males that are 7-10 years of age, have less than 5 micron variation between the primary and secondary fibers, and present strong, healthy fibers that have not coarsened. These are the genetics for the future rather than a blue ribbon winner in a class of 3.

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