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Utility of Histograms

The US alpaca industry's obsession with micron reporting and histograms began early, and is reflected in a number of articles that appeared in the ARI Journal between 1996 and 1999. Whether this reflects sound science or culture is arguable.

Several articles have been written about the relationship between nutrition and fleece fineness in sheep, goats and alpacas. George H. Davis wrote about a study done on alpacas at the Tara Hills High Country Research Station in the South Island of New Zealand in 1989 (see, "Alpacas Are Just Fine - Should They Be Finer?" in the WINTER-SPRING 1996 issue of the ARI Journal)

"...measurements were made annually at shearing each October At Tara Hills the alpacas grazed irrigated ryegrass and white clover pastures. Dr Wuliji's measurements showed that during the first two years at Tara Hills, the average liveweight increased to 68 kilograms, 51 percent heavier than the prequarantine weight in Chile, and the average fiber diameter increased by 6.8 microns, from 25.2 microns to 32.0 microns. In 10 percent of the flock, fiber diameter increased by more than 9 microns, 11.5 microns in the most extreme case."

An increase of 9 microns can easily move a fleece from the "Baby" class to the "Adult" class!

In his article "Fiber as a Transitory Medium: Factors Affecting a Histogram" (See WINTER-SPRING 1998 issue of the ARI Journal) Eric Hoffman wrote

In 1997 this ARI screener was afforded the opportunity to test a group of twenty-one alpacas (ten huacayas and eleven suris) on two occasions four months apart during a period of radical dietary change. The results demonstrate that some aspects of alpaca fiber measurement commonly recited on a histogram are easily altered, while other measurements remain relatively constant...To maximize their growth potential, the animals were introduced to a high-protein diet of unlimited amounts of high-grade alfalfa and a carefully regulated grain/pellet supplement. Four months later fiber samples were collected from twenty-one of these animals (ten huacayas and eleven suris). In the 4-month period between the original sample and the second sample the animals had...[as a group] experienced an increase of 3 microns in diameter, moving from an average of 21.8 to 24.8 microns, with an individual animal skyrocketing 9 microns in four months. The percentage of micron counts over 30 in the sample increased by a whopping 10.7 percent, from 6.7 percent to 16 percent.

Results such as the above should give the alpaca breeder pause for thought when presented with micron reports as evidence of an animal's quality. The experienced eye will know that histograms reflect a combination of environment and genetics, the two of which are difficult to separate.

So, does this mean that objective measurement of alpaca fleece is useless. No, it simply means that its utility is limited. A histogram can be a good tool when used in the correct way. Comparing animals in the same herd subject to the same environmental influences over the period of fleece growth can, for instance, be fairly compared to each other in a relative sense.

But, to rely on a histogram as an absolute measurement of the fiber genetics of an animal is a false hope, especially when the test results fall within a range of 4-7 μ's. In other words, given the results quoted above, an animal claiming an average fiber diameter of 20 μ could measure in the 24-27 μ range on a richer diet!

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