Using OFDA2000 Fleece Measurements for Genetic Improvement in the NSIP

By D. R.  Notter, L. A. Kuehn, R. C. Borg from the Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University and R. W. Kott from the Department of Animal and Range Sciences, Montana State University

July 2005 -- A project, funded by the American Wool Council, has laid the groundwork for the incorporation of OFDA2000 (Optical Fiber Diameter Analysis 2000) fleece measurements into National Sheep Improvement Program (NSIP) genetic evaluations. Results clearly demonstrate that many of the OFDA measurements are highly heritable and would be expected to respond favorably to selection.

Expected progeny differences (EPD) for yearling-fleece traits were likewise shown to be strongly related to fleece characteristics in adult ewes. EPDs for lamb-weaning weight and ewe prolificacy were not associated with OFDA fleece measurements, suggesting that these production traits can be improved without negative effects on fleece value. These results indicate that OFDA2000 measurements can provide a new level of accuracy and detail in the evaluation of American wool, and can serve as a powerful tool for genetic improvement.

Measurements

The study utilized OFDA2000 measurements on 186 yearling and 847 adult Targhee fleeces from six flocks enrolled in the NSIP. Measurements included in the analysis were:

• micron average: the average fiber diameter in the sample;
• micron standard deviation (SD): the SD of fiber diameter within the sample;
• micron coefficient of variation (CV): the CV of fiber diameter within the sample (both micron SD and micron CV are indicative of the uniformity of the fleece);
• comfort factor: the percentage of fibers that are less than or equal to 30 microns (the percentage of fibers >30 microns - the ??prickle factor?? - is associated with the scratchiness of the fabric);
• spinning fineness: a measure of the performance of the fiber when spun into yarn that considers both the micron average and the uniformity (micron SD) of the sample;
• staple length: length of the staple in millimeters;
• SD along the staple: the SD of fiber diameter along the staple, a measurement of uniformity of fiber diameter during growth of the wool fiber; and
• curvature average: a measure of fiber structure that is related to crimp frequency (higher values for curvature indicate more crimps/inch).

Average OFDA measurements for yearling and adult ewes and heritability estimates for each measurement are shown in Table 1. Heritability estimates are high (??0.50) for many of the measurements, indicating opportunity for rapid genetic improvement from selection. In particular, the relatively high heritability for micron SD and CV indicates opportunity to genetically improve fleece uniformity, and the high heritability of curvature indicates opportunity to select for desirable crimp structure. Only the

SD along the staple had an estimated heritability of less than 0.3, suggesting that this measurement mainly reflects effects of environment, management and physiological state.

Table 1. Averages for OFDA measurements in yearling and adult ewes

Associations between OFDA measurements in adult ewes and NSIP EPDs were evaluated for the following production traits:

• weaning weight;
•  maternal milk (an indication of genetic merit for mothering ability that reflects genetic differences in ewe milk-production potential, as realized in its lambs and expressed in pounds of lamb weaning weight);
•  yearling weight;
•  yearling fleece weight;
•  yearling fiber diameter;
•  yearling staple length;
• percent lamb crop (number of lambs born per 100 ewes lambing).

Results

Results of this analysis revealed that EPDs for yearling fiber diameter were very closely associated with OFDA fiber diameter measurements in adult ewes. A one-micron difference in yearling fiber diameter EPD was associated with a 1.08-micron difference in OFDA micron average, suggesting a near-perfect genetic association between fiber diameter measurements in yearlings and adults. Weaning weight and percent lamb crop EPDs were essentially independent of OFDA fleece measurements, indicating that selection for increased lamb production need not have antagonistic effects on fleece value. The maternal milk EPD (an indicator of ewe milk production) was found to be favorably associated with both fiber diameter and fleece uniformity.    

As access to OFDA evaluations of individual fleeces expands, there will be corresponding oppor­tunities to incorporate these measurements into industry genetic-evaluation systems such as NSIP. The incorporation of OFDA measurements into NSIP will be relatively straightforward once the specific measurements that largely contribute to specification of fleece value are identified, and once the emphasis has been placed on the selected measurements.

This research was funded by the American Wool Council and was made possible by the cooperation of Targhee breeders who contributed wool samples and NSIP production records to the project.

How this Research Benefits the Producer

"This research is very exciting and positive for the U.S. sheep industry, as it demonstrates that producers CAN have their cake and eat it too ?C increased ewe productivity, heavier weaning lambs and wool traits can all be simultaneously selected,?? says Bob Padula, wool quality consultant for the American Sheep Industry Association (ASI).

Because wool traits are highly heritable, producers can make better informed and earlier selection decisions for replacement animals and fine tune their wool selection program using individual animal data based on sire information.

Even though wool fiber diameter changes over the course of time, this project demonstrates, from a genetic-selection standpoint, that measuring 12-month-old animals one time is sufficient to know what kind of genetics they will pass on to their offspring.

??Only needing to test the individual animal once in its lifetime is a direct financial benefit to the producer,?? says Padula. ??For those producers not involved in NSIP, the information suggests that after testing your replacements, the ??genetic rankings?? of your animals within your flock probably do not change.??