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Let's Talk about Fleece: Genetics and Nutrition

Originally published in the June 2000 issue of Marker, quarterly magazine of the National Colored Wool Growers Association. Reproduced here with permission. See also Part 1, The Basics and Part 3, Harvesting and Handling.

Wool is keratin, the same protein found in hair, nails, and horns. The structure of the fiber allows for moisture absorption, flame retardation, insulation, and resilience. Wool production is largely dependent on fleece weight and staple length.

The quality of the fleece produced begins with the real producer - the sheep. While there are things about a fleece that we can improve, there are other things that we cannot change and have no control over. Some things about an individual sheep's fleece that we cannot change include:


All things equal, wool type and quality is genetically determined. The ewe, but especially the ram, should have the genetic capability of producing top-quality fleeces of their own in order to produce lambs with superior wool. Wool traits are highly heritable. Heritability estimates are high enough that the mating together of the best individuals for two traits alone, fleece weight and staple length, should result in fleece improvement. Other highly heritable traits include yield, fiber diameter, density, color, and medulation.

Genetic Influences
  • Breed: The fleece characteristics of grade, crimp, staple length, and lock formation are breed-related. They can range from Merino at one end of the spectrum to Karakul at the other. The merino fleece is characterized by having the finest grade or smallest diameter of fiber, the most crimps per inch, a short staple length (slow growing fibers), and little if any lock definition. This is called a closed fleece and it can shed water. The fiber from the Karakul can be more than twice the diameter of the merino and is a coarse, braid or carpet grade of wool. Often double-coated, the Karakul fleece may forego crimp completely for soft, loose waves with long staple lengths and definite lock formation (termed an open fleece).
Double Coated Karakul Fleece
Double Coated Karakul Fleece

  • Uniformity: As we look at the fleece on the sheep, the best wool will be over the shoulders and along the sides. A good fleece will maintain this same quality, with little or no variation, over the back and rear-end, and should carry down to the top of the legs and belly. A poor fleece will have variation in quality, like grade and crimp, especially over the legs and belly. Britch wool on the thigh area could be very coarse with hair-like texture, while belly wool will be short and dissimilar.

  • Color: White fleece should be a bright white or cream, never yolky-yellow or dingy tan. Natural colored fleece can be any color other than white, but should still be bright.

  • Luster: Fleece luster is the inner translucent glow or an outer reflective shimmer. This single attribute makes an ordinary fleece come alive and become an award-winning fleece.
Inherited Deficiencies

Wool faults are defects that lower the value; breeding faults can be controlled. The following list shows major inherited deficiencies:

  • Hairy or Medullated wool: These are coarse, straight, chalky fibers, with a thick medulla or core and a thin cortex or outer layer.
  • Kemp: Kemp are short flat fibers have sharp pointed tips and are not medulated. They also have a chalky, often kinky appearance. These fibers shed and give tweed cloth its characteristic pattern.
  • Pigmented fibers: Colored fibers in white wool limits its usage and lessens its value.
Sheep Management

Some things about a fleece we can change and have the power to improve, including:

Nutrition: Poor nutrition results in poor fleece growth, thin, fine, wispy, harsh, and brittle wool. Good nutrition can result in dense, lustrous growth, with great handle and spinability. A balanced diet is essential and should be maintained year-round. A mixed-grass pasture, or hay, is ideal, but should always be supplemented with a free-choice salt/mineral/vitamin mix, as well as clean water.

Wool consists of two main fractions: the wool fiber and the yolk or grease. The fiber is practically pure sulfur-containing protein. The grease fraction is made up of a water soluble fraction called suint and a water insoluble fraction called lanolin. Nutritive requirements for wool production are over and above those needed for growth and maintenance, in fact these requirements can be considerable. The primary requirements needed for wool production are sulfur-containing protein, energy, potassium.
Factors for fleece growth
Feed >
Fermentation in the rumen >
Nutrients absorbed into the blood stream >
Metabolic pool >
Raw materials and energy for wool growth,
including Primary follicles and Secondary follicles.

We can start supplementing the ewe diet with additional protein early in gestation to select for 'secondary follicle' development, as discussed in Part 1. Increasing the numbers of secondary wool follicles can result in denser fleeces. At about 90 days into gestation these secondary follicles are formed. They can produce as many as eight fibers from one follicle, if the conditions are optimum. These follicles also produce finer fibers and lack the sweat glands found in the primary follicles.

In contrast the �primary follicles', produced earlier in gestation (between 50-90 days), result in only one fiber being produced and that one could be a medulated fiber. They also contain sweat and sebaceous glands. In the birth coat the presence of halo hairs, sickle fibers and some types of curly-tips are associated with primary follicles, while the preferred later maturing curly-tips and histerotrichs are associated with secondary follicular development.

Energy Feeds vs High-Protein Feeds

If we want to boost the protein levels to the pregnant ewe, for instance, without getting her too fat, we could select high protein meals in a pelleted form. If energy is needed for growth or fattening then we could select from the list of energy feeds with high total digestible nutrients. See Table #1 - Feed Type.

Table #1 Feed Type
Feed TypeTDN
(Total Digestible Nutrients)
Protein Levels
Energy Feeds
Shelled Corn78%9%
Wheat Grain78%12%
Wheat Bran63%9%
Protein Feeds
Fish Meal68%60%
Soybean Oil Meal72%44%
Cottonseed Meal74%44%
Peanut Oil Meal70%45%
Linseed Oil Meal74%35%

  • Corn is the most widely used feed grain, and is the best energy feed. Corn should be supplemented with a protein feed.
  • Oats are not a good fattening feed, but are higher than corn in fiber and protein.
  • Wheat bran is a by-product of the manufacture of wheat flour. Its primary use in livestock feed is a source of bulk, as a mild laxative, and is a source of phosphorus. It can be both a source of energy and a source of protein. Its use in feed is usually limited to 10% of the ration.
  • Soybean oil meal is a popular and excellent source of protein.
  • Fat-extracted Flax seed (Linseed Oil Meal) is excellent for putting the bloom on show animals.
Health: A healthy sheep feels good, has a healthy appetite and grows the best fleece it is capable of producing. Stress, lambing, illness, weather and parasites all put a burden on the production of a beautiful fleece and often results in weak or tender fibers. Breaks in Wool Locks
Breaks in Wool Locks

Environment: Burrs, thistles, dirt, mud, hay, chaff, manure, sun, and heat will decrease the value of wool on a sheep. Keeping sheep on clean pasture, but with access to shade, will eliminate many of the damaging factors. A good hard cool rain will do wonders for a fleece, as long as the weather is not hot, steamy and humid. During the latter conditions, sheep seem to love to find something to rub on. And we know what water, heat and friction does to wool: it makes felt.

To Summarize

In order to improve the wool on our sheep we must:

  1. Maintain a good selection program, remembering that wool traits are highly heritable.
  2. Provide adequate nutrition; the last trimester is very important for both the ewe and her unborn lamb.
  3. Control internal and external parasites as well as other diseases.
  4. Control vegetable matter contamination.
  5. Shear or at least crutch ewes before lambing.
Once we have that perfect fleece on our sheep what do we do next? See the next article, Harvesting and Handling the Fleece.

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