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Understanding and Interpreting Micron Testing

by Angus McColl

The integrity of sampling - the careful and proper selection of a sample - is the most critical factor involved in measurement of diameter and other fiber measurement in individual animals. The samples must be taken at the middle of the side in the blanket location. (See Figure 3.12 in the ARI screening manual, published in this issue.) The sample should be uniformly cut as close as possible to the skin level, which is the base of the staple, and should be no smaller than 2 square inches in size. The sample should be kept in the staple configuration, which is its natural growth state. It should not be brushed out, cleaned up, or folded. Flat-bladed shears (such as round-tipped Fiskars scissors) or clippers are recommended as the safest tools to use in taking samples.

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Length of Fiber Sample

Maintaining the staple formation of the sample submitted to the laboratory is important for a practical reason: The 2-millimeter sample used for measurement in the Laserscan is cut close to the base of the staple to measure fiber that has grown side by side under the same environmental conditions. These conditions include level of nutrition, pregnancy, lactation, and stress caused by sickness or trauma. The coat of a recently shorn animal generally has not been exposed to highly variable environmental conditions, so environmental influences on varability of fiber diameter will have been minimized. Working with staple lengths shorter than 1 1/2 inches is problematic because the staple configuration breaks down and we are unable to take an even cut across the base during sample preparation.

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Packaging and Identifying Individual Samples

Once the 2-inch-square sample is taken, it should be placed in a plastic sandwich-size bag and clearly labeled with the following identification:

Identification numbers (ear tag, microchip, and/ or registration) Age (date of birth is preferable to age in years) Sex (male, female, gelding) Phenotype (huacaya or suri) Date of sampling

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Major Factors Influencing Fiber Diameter

Three factors have primary impact on fiber diameter: age, sex, and level of nutrition. As an animal matures, its fiber tends to have a higher or coarser micron value. Males frequently possess a higher micron value than females. The level of nutrition affects fiber diameter results because overfed animals produce higher micron values than those on a maintenance diet. This does not mean that animals should be underfed to produce finer fiber. An unsound or unhealthy animal is a poor risk in a breeding program regardless of its fiber diameter Underfeeding causes significant negative side effects, such as lowered fertility, lower birth weights, and higher cria mortality rates. The safer course is to maintain alpacas on a thrifty but nutritious diet that maintains a healthy body condition to produce fiber that lives up to its genetic potential, by following the animal husbandry practices suitable for your farm's location and the advice of a veterinarian familiar with camelids.

Genetics and selection are also fundamental to producing sound animals with fine fiber. The alpaca samples included in our Laserscan database since June 1994 indicate that a broad genetic base exists in the U.S. alpaca population. A diverse genetic base creates opportunities for selection of desirable traits, including fiber fineness. But a word of caution is in order: In animal selection, focusing on one particular trait increases the risk of negative traits that may be linked to the one being selected. For example, focusing for fiber fineness may inadvertently select animals with small body size and low fleece weights.

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Understanding Laserscan Micron Test Results

Samples tested by Laserscan yield a micron test report, examples of which are shown in Figures 1 and 2.

At the top of the report is administrative information provided by the identification submitted with the individual sample. The histogram displayed on the report depicts the measurement of 2,000 fibers in scale. The histogram is the most common graphical presentation of quantitative data; in the micron test report, the variable of interest, fiber diameter in microns, is placed on the horizontal axis, and the relative frequency values (percentage of fibers observed within a micron measurement) are shown on the vertical axis.

Depending on the height of the results, the histogram is printed on either a 12% or 24% scale to fit our letter-size report format. The bottom line (horizontal scale) is measured in 1-micron increments (one micron is equivalent to one thousandth of a millimeter or one twenty-five thousandth of an inch).

To analyze the micron test report histogram, find the average fiber diameter (AFD), "Fiber Diameter in Microns," on the horizontal scale. Standard deviation (SD) is a term representing an average of individual deviations (plus or minus micron values) from the mean, of the average fiber diameter. The smaller the standard deviation, the more uniform the population of fibers measured will be.

Standard deviation is the most stable of variability measurements and is used in the computation of other fiber statistics, such as the coefficient of variation (CV). This value, used in the statistical analysis of different populations of fiber (different animals), is the standard deviation divided by the average fiber diameter multiplied by 100 and reported as a percentage.

The uniformity of two alpacas' fleeces with different average fiber diameters is illustrated by the following results (see Figures 1 and 2):

Figure 1. Micron Test Report, Test #1

Figure 2. Micron Test Report, Test #2

Statistic Test #1 Test# 2

AFD

22.7

23.9

SD

5.0

5.0

CV

22.0

20.9

The animal with the more uniform fleece is shown in Test #2: It has the lower CV but a higher AFD. The percentage of fiber greater than 30 microns is also included in the report. In commercial application and breed selection, this data is of interest because it shows the coarse edge that determines the final use of the fiber. It has a relationship to the strength of the yarn processed from the raw fiber and influences "prickle" factor, the scratchy quality associated with coarser fibers.

Both the date of birth and the date the sample was taken must accompany the report to identify the age of the animal. A test report not including the sample date is not as helpful as one confirming that the test results represent fiber taken when the animal was a specific age.

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A Marketing and Genetic Selection Tool

When utilized properly, objective fiber testing can be a powerful marketing and genetic selection tool. Objective measurement is an assessment made without the influence of personal feelings or prejudice. Visual appraisal and fiber handling are fundamental aspects of fiber judging but very weak appraisal methods of accurately identifying fiber diameter. Instrumentation can accomplish the measurement of fibers within a micron. Because the measurements are so tiny, the difference between a sample at 20.5 microns and one at 22.5 microns is small mathematically but critical in commercial use and pricing structure.

Based on this factor alone, fiber-testing technology gives breeders a useful tool to analyze fiber and track the progress of their selection programs. The determination of average fiber diameter helps identify the best end use for fiber and is information that mills require before making their purchasing decisions. The ability to provide information on fiber quality places alpaca producers in a stronger position to receive what their fiber is worth. Very few people buy and sell commodities without knowing everything they can about them. Information is power in the marketing world, and objective fiber assessment provides it. But from the perspective of the fiber-testing facility, the micron test is only as good as the sample and the information submitted for testing. The laboratory cannot jeopardize its integrity by providing results from improperly taken samples, either by location or size. Breeders have the same interest in maintaining their reputations with high-quality animals and by keeping accurate records of their overall performance.

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David Kabbai - 619.890.9297 - 1.877.611.1319