Measurements of Mean Fiber Diameter for the EPD Program

The following document was provided to the ARI Board of Directors in 2009 as the Board sought expert opinions on the discussion of use of butt (base) cut testing versus staple length profile testing for use in an Expected Progeny Differences program.

Dr. Chris J. Lupton
TexasAgriLife Research
November 4, 2009

For this program, the ARI Board members have apparently agreed to use measurements made on samples shorn from the mid-side of the animal based on the assumption that these will provide reasonable estimates of the measured characteristics in the fleece as a whole (or at least the saddle portion). This being the case, the useful and practical options for sub-sampling and measuring the side-sample are somewhat limited.

  1. Guillotine at the base of staple and measure resulting snippets with an OFDA 100 or a Laserscan instrument.
  2. Minicore the whole staple and measure as above.
  3. Measure the intact staple using an OFDA2000 instrument.

Assuming a 12-month staple is being measured, options 2 and 3 normally provide very similar results for mean fiber diameter (MFD), standard deviation of fiber diameter (SD), and coefficient of variation of fiber diameter (CV). The values are means for one production year as influenced by increasing age, production status, and changes in the environment. In contrast, information generated by option 1 is representative of a relatively short period of time (i.e., the time it takes to grow 2 mm of fiber) that can be accurately associated with animal age. Consequently, the option 1 MFD, SD, and CV results for a particular staple would typically be quite different from those obtained by options 2 and 3. In particular, the CV values obtained using options 2 and 3 would invariably be greater than those obtained using option 1 because they include along-fiber age and environmental components of variability in addition to the inherent genetic differences among fibers. For samples taken from contemporary groups (i.e., animals of similar age, managed alike and sharing the same environment) of young growing animals (e.g., 1-, 2-, or 3-year-olds, for example) that are becoming progressively coarser as they age, MFD results from base of staple (option 1) would invariably be coarser than those obtained using options 2 and 3 because these latter are actually estimating MFD for average ages of 6 months, 1.5 years, and 2.5 years old, respectively.

To minimize the influences of environment and age, and in an attempt to isolate the genetic component of a particular trait, data used in EPD calculations are obtained from contemporary animals. Because option 1 minimizes the effect of environment on MFD, SD, and CV, it is the logical choice for a genetic evaluation program. Further, an individual animal’s deviation from the mean of its contemporary group plus corresponding information for relatives (e.g., sire, dam, siblings, etc.) are all used in the complex calculation of EPD values. From this consideration also, and because we know that different sampling and measuring options produce different results, it would seem prudent to use a single method for sampling and measuring MFD, SD, and CV.

Finally, it is my understanding that since the first alpacas were imported into the U.S., option 1 has been the universal commercial method of sampling and measuring fiber fineness and variability. Assuming historical data are to be used in the ARI EPD database, again it would seem to make the most sense to continue using option 1 methodology.

If the ARI Board and individual breeders were to decide to use data obtained via all 3 options in the alpaca EPD program, then it would be advisable, for the multiple reasons outlined above, to use a unique identifier for EPDs calculated using the different types of measurements. Failure to treat these measurements separately would reduce the accuracy of the EPDs.

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