Section 2.71: Density

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Technically, alpaca fiber density is a sampled measure of the number of hair follicles per square millimeter of skin. The number of follicles is measured quantitatively using a skin biopsy. In a skin biopsy, a small core of the alpaca’s skin, about the size of a pencil eraser (10mm/0.5 inch), is taken from the alpaca's mid-section and then evaluated scientifically in a lab to produce a specific density measurement expressed in terms of primary and secondary follicles per square mm. 

While density can be estimated by hand and through some visible indicators, results can be inaccurate. Some breeders evaluate density by grabbing a handful of fleece and assess density by feel. This method can be handy for comparing one animal to another, to obtain a qualitative sense of which is more dense. In the show ring, judges do this all the time, often bringing the animals side-by-side to compare each to the other in terms of fineness and density. Individual Huacaya staples or Suri locks can also be assessed , both visually and by feel, to evaluate the amount of material within the staple or lock, thereby estimating an animal's overall density. These sensory methods, however, are fairly subjective and a significant amount of experience is required to accurately estimate an alpaca’s fiber density by hand. To the inexperienced, a handful of 40-micron fiber would tend to fill the hand easily and may produce the illusion of a very dense fleece. To the untrained hand and eye, a coarse alpaca can feel both soft, perhaps due to fiber uniformity, and dense. In contrast, a handful of 16-micron, ultra-soft fiber can feel very lightweight, which may result in an inaccurate assessment that the fleece is not very dense. The "take-away lesson" here is that, density is very tricky to measure qualitatively and requires a great deal of practice to do so accurately.

  • Visual clues to density include compact, solid staples, with little skin visible upon parting the fleece. Often only a thin jagged line of skin shows in the fleece of a very dense animal. Very fine fiber can produce the illusion of a lightweight, less dense fleece. Excellent fleece coverage on the legs and head, including a thick topknot and full cheeks, may be indicative of density. Consistency within the fleece also often goes hand-in-hand with density. However, it is important to note that there are exceptions to all of these "indicators." For example, leg coverage on many high quality, very finely fleeced animals is often not as thick as on alpacas sporting coarser fleeces.Therefore, there are animals that may exhibit the indicators identified above, but nonetheless lack density. In general, however, these indicators are useful tools in our "breeders' toolkit." 

A highly organized lock or staple, exhibited by Suri twist or Huacaya crimp, may be an indication of density. The reason density matters so much to a breeder is that increased density results in increased shear weights, and therefore a breeder's profit from fleece sales increases as well. In addition to density, an animal's body size also impacts shearing weight. This is one reason why some have bred alpacas to llamas – to increase the size of the alpaca. The idea is to produce alpaca quality fiber on a llama’s larger frame. Although the strategy has resulted in bigger alpacas, in general the fiber produced is coarser. Quantity went up, but quality, in terms of a fine uniform fineness, went down. Essentially, a compromise was reached, which may or may not be considered desirable.

Some scientific studies indicate that fleece follicles tend to develop farther apart in large animals. This would reduce density. Sheep breeding history and analysis shows the densest fleeces in the Merino industry were on small to medium-sized animals with thick bodies. These animals also turned out to be most efficient grazers. They required less water and fodder to sustain their bodies. Bigger may not always better. Fine fiber sells for a premium, so quality can "outweigh" quantity when it comes to producing fiber for profit. An alpaca advertised as having produced 15 pounds in one shearing may sound impressive. However, if that fleece is high-micron fiber, not only will it naturally weigh more due to the coarseness of individual fibers, but it will lack the key advantage of alpaca, which is it's luxurious softness resulting from uniformly fine fibers. According to one source, an increase in AFD from 25-microns to 30-microns will cause fleece weight to double.

In addition to providing protection from the elements to secondary fibers, primary fibers are the building blocks around which density is built. The ratio of the number of secondary fibers to primary fibers (S/P ratio) becomes a highly valued statistic for analyzing a fleece for density. The higher the ratio between the number of secondaries to the number of primaries, the denser, softer, and more consistent the animal is likely to be. On a fleece where there is a low S/P ratio, the thicker primary fibers will be more noticeable as we run our hand along the fleece, as there will be few secondaries to contribute greater consistency and fineness. In an animal like this, the histogram will show an "average fiber diameter" (AFD) that is skewed higher. Studies show that, while there are exceptions, the denser the alpaca, the finer it will tend to be. Breeders should strive for a high S/P ratio of 15:1 or greater, which will generally result in better handle, lower AFD, and greater uniformity, while increasing fiber density. Increased density, combined with fineness, results in increased profits. 

While density usually goes hand-in-hand with fineness in alpacas, some animals can produce very dense fleeces that are not especially fine – Lincoln sheep are an example. In alpacas, density or a high S/P Ratio will generally result in fleeces that exhibit consistency in terms of both AFD, staple length, and crimp or lock style. In both Suris and Huacayas, the pressure of tightly packed fiber pushing outward together from skin follicles forces the fibers to align with uniform lock or crimp styles.

Why does density matter?

Focusing on density as a breeding goal, may be a better strategy than focusing on fineness alone. The majority of very dense animals have fine micron counts. It is not true, however, that very fine animals are necessarily dense. Extreme fineness alone may be counterproductive to maximizing a breeder’s profits. While vicunas are incredibly fine, with amazing handle and uniformity, Vicuna fiber is not as strong, durable, warm, or water resistant as alpaca fiber. As a result, it is not as commercially marketable as alpaca. In the worldwide sheep wool industry, breeders have found that focusing on fineness alone results in a loss of staple length over the course of four generations, which reduces overall shear weights and, therefore, profit.

There are 4 ways to increase blanket weight

  • Breed for increased follicular density
  • Breed for increased staple length
  • Breed/feed to increase the micron count
  • Add or leave dirt in a fleece

Clearly, of the above options, only the first two make good sense. From the perspective of producing fiber for profit, we want to breed for increased density and a good staple length. If successful, these attributes will result in quality (fineness, uniformity) and quantity (fleece weight), thus maximizing profit.

a. Tips for a Subjective Density Analysis

When analyzing an animal's density look for:

  • Small, tightly packed bundles or staples of uniform fibers.
  • Bright fiber – generally fibers with lower scales appear brighter; light reflects differently from high scale edges and dust is caught in the scales, dulling the appearance of the fiber.
  • In Huacayas, a well defined, uniformly expressed crimp from skin to the tip.
  • Less contamination inside the fleece (look at the shoulder fiber for this evaluation as the fleece ages), as dirt and dust are less able to penetrate a very dense fleece.
  • Lack of obvious primary fibers, which is indicative of

uniformity among fibers as a result of density.

  • Staple thickness and resistance, when pressed between your fingers; staples should be three dimensional instead of flat.
  • There should be no cross-fibering (fly away fleece) in dense fiber. There are rigid rules for growth in dense fiber and little "room to roam."
  • Extension of blanket fiber characteristics into the shoulder, neck, chest, belly, and/or upper leg areas.
  • "Cracks" in the fleece – dense fleece often appears to crack open, "like a book."
  • Dense fleeces frequently present more resistance when opened.
  • Look for a thin, jagged line of skin at the base of the fleece; the more skin showing when the fiber is opened, the less dense the animal.
  • Long staple length, which can be indicative of density.
  • Pressing down to feel if there is resistance between the outside of the fleece and the backbone is an indicator of density only if the fleece is also fine. A wire hairbrush will provide a great deal of resistance, but that's because it is stiff, not dense.
  • Grab a handful of fleece at the side; with experience and through practice comparing animals with known fleece characteristics, this can become a useful gauge of density.

b. Considerations for Objective Density Analysis

There are a number of factors that relate to the scientific measurement of density:.

  • Follicles generally appear in groups of between 15 and 50. The more follicles per square millimeter, the denser the animal.
  • If the fleece is dense, the fibers within each follicular group will grow in a highly aligned fashion.
  • The relationship between the para and ortho cortex determines the crimp style. The hard protein keratin bends the fiber and the soft keratin reacts to it.
  • In a very dense alpaca, primary fibers (as well as secondary fibers) do not tend to be as coarse simply because of the competition for nutrition within a finite area of skin.
  • The ratio of stretched fiber length to un-stretched staple length is a key measurement. The goal is 1:1.2, which means that the fiber can stretch 20% farther than the un-stretched staple. This indicates the crimp is deep, which translates to greater elasticity.
  • The coefficient of variation (CV) should decrease as density increases, as we would expect the fibers in a dense fleece to be more uniform.
  • With density generally comes increased crimp definition. Crimp and the scales along the fiber shafts combine to reflect light, producing brightness in Huacayas. In Suris, it is longer scales and straightness that create luster.
  • Small clusters of pre-papilla indicate density and fineness. Large clusters indicate coarseness and less density.
  • The wax from the sebaceous glands, which coats each fiber as it gowns, gives alpaca fiber its water repellant properties and adds to the look of a well-nourished, bright fleece.
  • Dense alpacas may exhibit a wide variety of crimp styles, from "zipper" (low amplitude, high frequency crimp) to "French fry" (high amplitude, low frequency crimp).
  • Staples (naturally bundling groups of fibers) should stretch when pulled, indicating longer actual fiber length.

c. Factors to Consider When Breeding for Density

Finer primary fibers and smaller primary follicles are associated with increased follicular density overall.

  • Assuming each alpaca has a set number of prepapilla skin cells, the greater the number of secondary fibers using those prepapilla cells in a fleece, the fewer prepapilla cells available for the primaries. This translates to primaries that have fewer root cells and so develop thinner hair. Follicular development is thought to be mainly a function of genetics, but may also affected by nutrition and other environmental factors that can affect a growing fetus.
  • Some feel that selecting for narrow staples, rather than wide staples, may be another step toward improved density.
  • As fleece length increases in a highly dense animal, the crimp may tend to develop higher amplitude and lower frequency because it grows faster, although this is not always the case.
  • Follicle and fiber measurements from skin and fleece samples allow us to select animals that have fine primary fibers, high fiber density, and good staple length.
  • Based on lessons learned from the sheep industry, breeding decisions based on density factors alone are likely to lead to shorter staple lengths and higher micron fiber over the course of four generations or so. Similarly, breeding for fineness alone may lead to loss of density, short staple length, and lower shear weights.
  • Relying on either density figures or fineness alone is a recipe for long term breeding disaster!
  • Breeding for fleece weight alone is likely to result in increased micron count and shorter staple length, which may not be a good trade-off if you are trying to increase profit from alpaca fiber production.
  • What breeders should do is select for fast growing fiber, with long staples, and high follicular density, which will generally deliver:
  • More fiber
  • Finer fiber
  • Greater fiber density
  • Greater uniformity (low CV)
  • A narrower range of micron variation over time (lingering fineness)
  • Brighter fleece
  • Less soil and parasite penetration
  • Fiber that is better suited to processing into high-end textiles

Summary: With experience and practice, density can be visually estimated by the amount of fiber in a staple. Most dense animals are also fine. However, many fine animals are not also dense. If fiber is too fine, it will not be as strong, durable, warm, or water resistant. Dense animals are more resistant to skin parasites (e.g., ticks) and to contamination by dust, mold and pollen that could cause allergic reactions. When there is less dirt in a fleece, the fleece will appear brighter. Coarse fibers have shorter and higher scales, which can trap dirt and contribute to making the fleece seem dense and heavy.

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