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Economically Relevant Wool Traits and Wool Heritability

Small group of white sheep in a sheep shearing enclosure.
Courtesy: Canva

Written with contributions by Heidi Carroll, former SDSU Extension Livestock Stewardship Field Specialist & Beef Quality Assurance Coordinator.

In 2020, South Dakota produced 1.65 million pounds of wool with a total value of $2.64 million, continuing to make South Dakota a top wool-producing state. Prioritizing the quality of this commodity can make wool a significant revenue source. Identifying and selecting for economically important wool traits improves production and is key in meeting your operation’s objectives. As wool producers, continuing to improve the national wool clip is important for profitability and sustainability of the entire industry.

Objective Measures of Wool

Economically important wool traits that can be objectively measured are: fiber diameter, staple length, fleece weight and clean wool yield.

  • Fiber Diameter: The average thickness of the fibers measured in micron (µm). Larger values denote coarser, and smaller values indicate finer wool. Average fiber diameter is a primary determinant of value and end uses. Coarse wools typically go into yarn, carpet and other thick wool products. Fine wools are used for close-to-skin application, like undergarments and active wear. Furthermore, fine wool has a higher commercial value than coarse wool.
  • Staple Length: Target staple length is approximately three inches. Generally, staple length is categorized into staple (≥ three inches) or clothing (< three inches). Generally, if average staple is shorter than three inches, uses are limited, and wool price is heavily discounted. However, overgrown wool (≥ five inches) can cause manufacturing difficulties during carding and combing and may also be heavily discounted. Staple length is also determined by strength of the fiber. Weak (tender) fibers break during processing, resulting in shorter fibers. In quantitative wool sample results, fiber strength is reflected as Newtons per kilotex (N/ktex). In the U.S., staple strengths less than 24 N/ktex are considered tender and 30 N/ktex is considered sound.
  • Fleece Weight: Average fleece weight in South Dakota in 2020 was seven and one-half pounds, according to USDA-NASS. Generally, coarser fleeces are heavier than fine wools. Fleece weight is expressed as grease fleece weight (pre-scouring) and clean fleece weight (post-scouring). Wool prices are based on Australian clean fleece prices.
  • Clean Wool Yield: Yield is expressed as a percent of usable fiber (clean wool) based on grease fleece weight. Greater amounts of grease, vegetable matter and dirt decrease yield. Breed and environment also heavily influence yield. Higher yields mean a higher percentage of clean wool, thus greater value.

Wool Heritability

Wool traits are moderately (20–40%) to highly heritable (≥40%), so improving quality and quantity of a wool clip can happen even after one generation. Heritability estimates the variation in a trait that can be explained by genetics versus the environment. In other words, a heritability of 0.4 means that a trait is influenced 40% by genetics and 60% by the environment. Selecting rams and replacement ewe lambs that meet the goals for an operation is the most-effective way to improve and increase wool productivity. However, it’s important to stay away from single trait selection, because if traits are negatively correlated, selection for one trait may negatively impact another. For example, selecting sheep solely with the goal of decreasing fiber diameter may decrease fleece weight, staple length and yield.

South Dakota is known for a high reputation wool clip. Continued emphasis on economically important wool traits coupled with careful genetic selection will help promote production, profitability and sustainability. Identifying key goals for your fleece quality is the first step in enhancing your overall clip.

Table 1. Wool Trait Heritability

Trait Heritability
Variability of fiber diameter High
Face covering High
Staple length High
Crimps per inch High
Skin folds High
Fleece weight (greasy and clean) Moderate to high
Yield Moderate to high
Fiber diameter Moderate to high
Fiber density Moderate to high

Adapted from SID Sheep Industry Handbook Vol. 8, 2015

Related Topics

Meat, Wool and Dairy