Butt (base) Cut vs. Staple Profile

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.

Fiber Testing for Genetic Improvement: Butt (base) Cut vs. Staple Profile

By Dr. Robert Stobart
Assoc Professor
Animal Science Dept
University of Wyoming

One has to be somewhat careful about using various technologies to predict fiber diameter of natural fibers with the view to use these measurements in genetic evaluation programs. There has been abundant literature produced that explains the effects of genotype X environment interactions and it’s their subsequent effect on the phenotype. Geneticists are adamant about minimizing this environmental effect to try to establish true genetic merit. I believe it is imperative that when discussing the genetic basis for diameter of natural fibers, that one disassociates the concept of fleece value from genetic potential. Producers need to establish for themselves the average diameter of the fiber being produced from their flocks and then utilize that information in their selection programs. They will also need to select for fleece weight once they have identified the fiber diameter average they want. Minimizing the environmental effects (primarily adequate feed resources) will allow the animal to express its genetic potential for producing fibers that meet the producers’ needs.

I’m not sure if you can equate the growth of fiber on an alpaca to that of the modern day sheep even though several researchers have indicated that pre-natal skin follicle development in alpacas is similar with the development of fiber follicles in sheep. The Australians have utilized airflow to estimate fiber diameter after the introduction of the airflow to testing wool in the late 1960’s. All the early work on developing h2 and genetic correlations was done using the projection microscope, see table 3.1 in Helen Newton Turners book on Sheep Genetics and also Dunlop’s 1962 article. If in reviewing these articles prior to the early 1990’s there are S.D. listed, these were obtained via projection microscope. There are consistent references to single cut (not referred to as butt cuts) and the difficulties in both time and cost in obtaining these measurements. The development of Laserscan and OFDA technologies, allowed for these technologies to replace the airflow when evaluating genetic relationships. These all are based upon utilizing a side sample and subsampling with 2mm core tubes the mid-side wool sample or in the case of the OFDA2000, taking a single staple of wool from the mid side or hip.

I believe this has been done out of the economics of measuring large numbers of animals and the view to look at “fleece value” rather than one of establishing true genetic merit. The general perception within the research groups in Australia is that the variation due to the environment and the genetic X environment interactions could be dealt with by statistical methods. There has been no literature to date that shows this premise is accurate. With the discovery of the “comfort factor, previously known as “prickle factor” it was thought that it was essential to measure the entire fleece (or side sample) to predict this fleece characteristic. However no research has investigated with alpacas the use of the variability within the side sample as determined by the butt cut and its’ relationship to comfort factor (comfort factor is calculated by subtracting percentage of fibers greater than 30 microns from 100).

The history of utilizing a single cut of fibers goes back into the 1920’s. Many workers have concerned themselves with the development of techniques and devices for measuring fineness and variability in wool. Barker (193I) described the work of early investigators in this field. During the past eighty five years, Hill (1922), Burns (I925), Duerden and Bosman (1926), Roberts (I927), von Bergen (1932, I935, 1936, 1942), Schwarz (1934), Hardy (1935) , Hardy and Wolf (1939), Granstaff (I940), Phillips et al. (I940), Pohle (I94O), and Wollner et al. (1944), have contributed to the literature dealing with the methods of measuring fiber fineness. Gorman (I93I) measured composite samples of Corriedale wool with a machinist's micrometer caliper and reported a mean thickness value of .000952 inch for the fibers measured. These techniques were modified and improved upon. Many researchers were using these modified methods in the late 40’s and 50’s, Pohle et.al (1953), Turner et. al (1953), Kyle & Terrill (1953), Wadley et.al (1949), Bertone and Landblom, (1949), Bailey (1949). Helen Newton Turner, described the method in a CSIRO report (1953). On page 10 of Dr. Turners Quantitative Genetics in Sheep Breeding (Turner and Young, 1969) she makes the statement, “The position of measurement  along the staple again depends on the measurement  technique; some, such as the airflow, may take the whole staple; the technique of measuring snippets permits sampling along the staple; the compressometer technique describe Wilson (1951) and Turner et al. (1953), which estimates fiber number and fibre diameter simultaneously, involves measurement at one point only. A point near the base is chosen in such cases; for selecting sheep within a flock, wool grown at the same time is then measured.”

von Bergen’s description of the “wedge method” of measuring the diameter of wool fibers was published in 1932, this particular method resulted in the development of ASTM standards D472-50T and D419-50T. D472 was known as Standard Specification & Methods of test for fineness of wool top, first published in 1941 and Standard Specification & Methods for test of fineness of wool, published in 1942. These standards came about because of the need of the U.S. Department of Agriculture, the US Customs Service and the Boston Wool Trade Association to use objective measurements to produce official standards for wool top and the overwhelming evidence that fiber diameter was the most important physical characteristic in the processing of wool and the characteristic which determined the economic value of wool. In 1926, the USDA developed grades for matching’s of grease wool based on diameter of the fiber. These were developed and promulgated to provide a common basis of understanding among growers, buyers, and others interested in the marketing, trading and processing of wool. They were originally based upon visual appraisal and this was becoming unworkable as the machines used to process wool were becoming more advanced.

These researchers were also interested in looking at the use of objective measurements in animal selection. The normal progression being that these methods were then utilized to start evaluating breeds and individual animals within breeds relative to the average fiber diameter of the wool being produced. Hardy published a paper in 1936 describing the need for objective measurements for breeding animals for selection purposes, it was necessary to know the mean fiber diameter and standard deviation. This was to be used by the U.S. Sheep Experiment Station in Dubois Idaho to aid in the selection of breeding animals.

Turner defines selection as any systematic process that results in different proportions of offspring being produced by different genotypes. This applies particularly to animal-breeding, where selection pressure for or against any phenotype can be high. They also go on to say that the value of a metric character is conditioned not only by the animal’s genotype but also by the environment in which it is reared. Since all animals cannot be at the same place at a given time, individual animals within a group must also experience different environmental conditions, so that even when animals are reared together, some of the differences between them are due to the effect of environment.

The Phenotype of an animal is thus a measure of contributions from both genetic and environmental affects and can be written: P = G + E.

To fully understand the genotype, the influences of the environmental effects must be accounted for if possible. By including the variation within a fiber in any model presumes that you can adequately account for the myriad of environmental effects that are influencing the diameter of the fiber at any particular time. Taking a sample and measuring the diameters of the fibers at one particular point, significantly reduces the environmental effects that need to be accounted for when compared to averaging the diameter of a fiber grown during the year. It is imperative that one separates the issue of “fleece value” from the determination of “genetic merit.”

Several refereed journal articles have been published, Dunlop & McMahon, Stobart et al., Iman et al. that indicate over 70% of the variation in diameter in a fleece comes from within—or across—staple fiber diameter, with along-fiber variation accounting to only 6% of the variation and among body locations making up the rest of the accountable variation.

When reviewing the literature regarding selection for fiber diameter in alpacas, a statement by McGregor and Butler supports other research findings that “sampling alpacas at ages <2 years is likely to substantially decrease selection efficiency for lifetime fibre diameter attributes”. Sampling young animals will provide data that is not correlated to their genetic capabilities after they reach 2 years of age. In sheep, diameter is not measured until the animal is at least 12 months of age, this is internationally understood. In Australia, prior to the establishment of numerous selection schemes, which by the way seem to disappear and new schemes replace them, rams were not measured until they were approximately 16 months of age.

My recommendation is to use one type of measurement for inclusion in an EPD program. I believe there is substantial direct and indirect information from reputable journals that would lean toward utilizing a single cut from a staple taken at a specific period (age) to establish the genetic merit of an animal to produce a fiber of a certain diameter (within its confidence limits due to instrument/operator error). I would like to emphasize that I have found no journal articles that can substantiate that utilizing the entire fleece to produce an average fiber diameter to be used in a genetic selection program is superior to utilizing a single cut taken near the base of the staple. I realize that there is a distinct lack of data that would confirm one method over the other and may be something to evaluate in a research project that the organization would be willing to fund.