|Using Objective Wool Measurements
By ROBERT PADULA
Wool Quality Consultant, American Wool Council
(June 1, 2009) With breeding stock sales on the horizon, now is the time for producers to review wool records and determine if they are satisfied with the wool performance in their flock and the income generated from wool. Even if one is satisfied with their current wool clip, to avoid “going backwards” in quality and quantity, consideration for wool is necessary whenever rams and replacement females are being selected. Not only is this important for producers that generate their own replacements, but it is important for growers that sell replacement ewes and rams to others.
Because wool traits are highly heritable, considerable progress can be made with ease by selection for wool. The opposite is also true, and if not careful, a wool clip’s value can decrease quickly. Because the ram contributes half the genes to all of his offspring, ram selection plays a significant role in determining the quality of the wool clip in a flock. Average fiber diameter (AFD) receives the most attention because it has the most impact on wool. If one is satisfied with their AFD, then they can focus on other issues such as staple length or pounds of wool.
When considering the use of wool objective measurement data for breeding and selection programs, some basics are important to remember.
Genetic change is accomplished by differences from the average. Within a flock, it is not uncommon to find an eight micron (or more) difference between the finest fleece and the coarsest fleece. For example, if a flock averages 24 micron, some sheep will measure 20 micron and some will be 28 micron. This isn’t necessarily bad, as it allows the producer to select for animals that are superior or above average, or not keep replacements from those that are less desirable.
When producers are satisfied with their wool, they can use rams that have similar wool traits and the quality won’t “go backwards.” However, if improvement of wool quality is desired, growers must select rams that are different from the average in order to move the wool trait for the flock in the direction preferred. The key point is knowing objectively the wool quality of the flock and what one wants to change.
Genotype vs. phenotype. Wool traits are highly heritable, and because of this, objective wool measurement data is a fairly good indicator of genetic merit or expression. However, only about 40 percent to 60 percent of what is seen or measured is due to genetics, the other part is dependant on how the animal was raised. Therefore, using an objective measurement is important to be able to determine what really has the potential to be passed on genetically AND also give an indication of what may or may not be genetically passed on to the offspring.
The challenge for growers is how to compare the genetic superiority of two rams at a sale when they are from two different producers? In reality, it’s difficult to compare them, but that does not stop anyone and it is done all the time. The important thing is being able to use the tools and information available to help producers make better informed decisions.
Ideally, sellers of rams should make performance records and wool objective measurement for AFD available on the rams they have for sale. Ram test data, National Sheep Improvement Program (NSIP) data and within flock/grower performance data all greatly help both the buyers and sellers of breeding stock. Without the objective wool test data and information being available, both the buyer and the seller are at a disadvantage. Objective wool test data provides the potential customer with information to be able to make better informed decisions regarding purchases that will help them meet their needs and requirements.
AFD, whether expressed as U.S. Department of Agriculture grades or in microns, can not be determined with a high degree of accuracy by parting the fleece and looking at the wool. Visual assessment of AFD, even by the “trained experts” is essentially a guess. Why? Because the AFD is the mathematical average of thousands of individual fiber diameter measurements and it is impossible for the human eye to look at a wool sample and calculate this. In addition, variation exists within a fleece:
- along the fiber due to changes in nutrition;
- between two fibers growing next to each other; and
- location on the animal (shoulder, side, britch).
There is more variation in fiber diameter within a staple or sample of wool than there is between locations on the sheep. Because of this natural variation, wool test data must be used as a guide, and never viewed as an absolute value.
Some people are better at guessing than others, but today’s U.S. sheep producers have access to equipment that is both accurate and economical for objectively measuring AFD. There is no right or wrong testing method, and one instrument isn’t better than the other. All the testing equipment used in the United States and any of the information provided by the wool testing laboratories is more reliable than looking at the fleece, but there will be slight differences between techniques and equipment. If the sample is run on the OFDA2000 equipment, the staple profile graph should be provided to show how the fiber diameter has changed along the length of the fiber.
A mid-side sample – centered on the third from the last rib, halfway between the mid-line of the back and mid-line of the belly on the left side of the animal – is a standard location for taking samples. Samples should be taken at the skin level and the entire length of the sample should be sent in for testing. Because animals under one year of age are still growing and developing, fleece measurements on young animals are not very reliable. Only animals older than 12 months of age should be sampled and tested. Samples should be taken on all animals at the same time and as close to the time of sale as possible. Samples taken 30 days prior to the sale will allow time for shipping, running the samples and return of the results.
The entire test report should be made available as well as information on all the animals that were raised in the same environment or peer group. This way, it can be seen how the individual animal performed in relationship to the others in the group and see if its performance is superior compared to the others in the flock.
Using the data. Within a seller consignment, if the rams are managed as a group, the objective measurement data of the wool can be used to compare and rank animals.
For example, a ram producer has 20 rams for sale and they average 24 micron. One ram has an AFD of 20 micron. How much ‘finer’ is he genetically than the rest of the group?
Remember, only a portion of the difference is genetic, the rest is due to how he was raised and other non-genetic factors. In addition, the ram only contributes half of the genes to the offspring, the other half comes from the female side. The Expected Progeny Difference (EPD) is that amount which will be contributed by the single parent.
The simplified calculation for EPD = half time the EBV, or in our example above the EPD would be:
-2.0 micron x ½ = –1.0 micron.
In other words, it can be expected that the offspring from the 20 micron ram to be one micron ‘finer’ than the offspring from the average 24-micron ram from that grower, even though he measured four-microns finer at the time of the sale.
Because different growers raise rams differently, the mathematical calculations above can not be used to compare rams between growers at a ram sale. Unless growers are involved in a coordinated breeding program, such as NSIP, comparisons are only valid within a grower consignment. If the rams were part of a centralized ram test, the data can be compared between the animals on the test – but only animals on test.
The bottom line, fiber diameter can not be visually determined with a high degree of accuracy. It is in the best interest of both sellers and buyers that objective wool measurement data is available on rams at sales so the buyers can make better informed purchases to advance the sheep industry.
For information on testing individual animal wool samples with the OFDA2000, contact the following:
Texas A&M University
Christopher Lupton, Ph.D.
(325) 653-4576 l firstname.lastname@example.org
Producers Marketing Cooperative
Ron Pope, Ph.D.
(325) 835-7173 l email@example.com
University of Wyoming
Bob Stobart, Ph.D. l firstname.lastname@example.org or
Brent Larson l email@example.com
University of Nevada, Reno
Tuman Wuliji, Ph.D.
(775) 784-4222 l firstname.lastname@example.org
Montana State University
(406) 994-2100 l email@example.com
OFDA100 and LaserScan Testing
For information on individual animal wool samples – washed, dryed and tested under standard conditions – contact the following:
Yocom-McColl Testing Labs
(303) 294-0582 l firstname.lastname@example.org