Butt testing versus Along Fiber testing
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.
Butt testing versus "Along Fiber" testing: A professional fiber tester’s perspective
By Paul Vallely
Australian Alpaca Fibre Testing
The purpose of this information bulletin is to outline the personal views of Paul Vallely, owner of Australian Alpaca Fibre Testing (AAFT) that relate to the measuring of fiber samples for the Alpaca Registry Inc’s (ARI) ‘Estimated Progeny Differences’ (EPD) Program. In particular, the bulletin focuses on the comparison of butt testing against the testing of the entire length of fibers (‘along fiber’ testing). Along fiber testing occurs with standard OFDA2000 measurements.
My views on this issue are in the main, based on 11 years experience as a professional provider of fiber measurement testing to the international alpaca industry and my involvement in a number of research projects and trials related to alpaca fiber measurement. Such testing services have been used for both breeding and management of alpacas.
The general aim of establishing EPD’s is to estimate the breeding value of sires/dams with respect to specific traits. The purpose of fiber measurement testing within the EPD program, is therefore a tool to determine, in as much as possible, the genotype fiber profile of individual alpacas.
The use of fiber measurement equipment is predominately confined to the measurement of the diameter of fibers, either expressed as an average or in terms of the degree of variation. Fiber testing data such as Comfort Factor, Standard Deviation, Spinning Fineness, micron profiles, histograms and Coarse Edge Micron are all derivatives of the measurement of fiber diameter.
Fiber length, curvature and medullation are obvious exceptions.
It is worth noting that both AFD and variation in AFD are reported as highly heritable and are economically significant traits.
AFD: It is a well recognized fact that diameter of animal fiber is an effect of both genetics and environment. While genetics might provide the base-plate for AFD, the degree of nutritional intake by fiber follicles (and the efficacy of the follicles) will determine the final expression of AFD at anyone time.
Therefore, the sensitivity of the butt section to environmental factors will be no different to the whole length of the fiber sample, irrespective of length or growing period.
Furthermore, given alpacas are managed under a range of geographies, seasons and regimes, the degree to which environment might influence AFD at any point in time or point in fiber growth, is not a constant.
Given the above, I can see no extra benefit of using butt testing when compared to measuring the entire length of the fiber sample (or part thereof) as occurs with OFDA2000 equipment when used in standard mode.
This is not to say that AFD does not have a place in evaluating the estimated breeding value of an alpaca. In fact AFD does serve a crucial part in evaluating progeny, however, nothing is served within this purpose by the use of butt testing.
Furthermore, there is no benefit within this purpose through the accumulation of measurements along the fiber apart from evaluating the sensitivity of an alpaca to its environment—and if this is the purpose, there are more effective ways to accomplish this aim.
Variation in AFD: The variation in AFD is expressed as either ‘standard deviation’ SD or coefficient of variation CV. While I personally prefer using SD when evaluating breeding stock, this bulletin will consider the general issue of variation of AFD.
Firstly, I suggest variation in AFD should be a critical value for alpaca breeding strategies. One of the major problems for converting alpaca fiber to yarn or fabric is the incidence of coarse fibers. Independent research has constantly shown that one of the most efficient and effective ways to combat this problem is through testing for variation in AFD. Coincidently, variation in AFD has been reported as moderately to highly heritable.
When the OFDA2000 reports SD or CV, it combines two forms of variation. One is the variation in diameter between the individual fibers in the samples which is generally regarded as genetically influenced (with some influence from pre/post natal nutrition). The other form of variation is the ‘along fiber’ variation.
‘Along fiber’ variation reflects the changes to the diameter of individual fibers caused by variations in nutritional intake by the fiber follicles. Generally speaking, this form of variation is of no help in determining the breeding value of a particular alpaca. In fact it can be obstructive in this regard. ‘Along fiber’ variation is almost purely a management tool.
For instance, an alpaca exhibiting a very high SD or CV reading from a normal OFDA2000 measurement report may in fact be an alpaca with a breeding value of very low variation in AFD, however, it may have been subjected to extreme changes in nutritional intake. In other words, it may have high variation along the fibers, yet low variation between the fibers.
Standard OFDA2000 measurements for variation in AFD are therefore affected by the environmental noise from ‘along fiber’ variation.
On the other hand, the use of butt testing provides a more precise measurement of ‘between fiber’ variation, as it measures one specified point on the fiber. This ‘one point in time’ measurement does not carry the environmental noise of ‘along fiber’ variation and therefore, is more precise with regard to estimating breeding values for SD or CV of AFD.
It should be noted the OFDA2000 in ‘100 mode’ is able to perform 2mm ‘butt tests.’
I personally believe, therefore, the use of butt testing is the preferred test method for the purpose of establishing EPD’s, given its superior precision when measuring variation in AFD. Specialized OFDA2000 testing software that can extract ‘between fiber’ variation is also suitable for this purpose.