Wool is the natural fiber harvested from sheep, measured by the weight of the fleece shorn from a single animal. The quantity obtained depends highly on biological and environmental factors, causing significant variation across the industry. Understanding the weight of the fleece is only the first step, as the raw weight is not the same as the final usable fiber.
The Average Raw Fleece Yield
The fleece weight immediately after shearing is known as “grease wool” because it contains natural oils, dirt, and debris. Annually, the amount harvested from one sheep ranges widely, from two pounds up to 30 pounds, reflecting the diversity of breeds and production methods. In the United States, the average raw fleece weight for a commercial sheep is approximately 7.2 pounds (3.27 kilograms) per year. Heavy-producing sheep, often bred for coarse wool, can yield fleeces consistently in the 10 to 18-pound range.
Factors Influencing Wool Production
Fleece weight disparity is largely explained by genetic selection and animal management quality. Breed type primarily determines both the quantity and quality of the fiber grown. Fine-wool breeds, such as Merino, typically produce fleeces with a lower overall weight compared to breeds selected for long, coarse wool. Coarse-wool sheep, like Lincoln or Romney, often yield the heaviest fleeces because their fibers grow longer during the annual cycle.
The greatest influence on wool growth rate comes from the sheep’s nutritional intake. A balanced diet with adequate protein and energy is necessary for the constant production of keratin, the protein that forms the wool fiber. Deficiencies in protein or minerals like sulfur can lead to weaker, thinner, and slower-growing wool, directly reducing the total fleece weight. Poor nutrition in pregnant ewes can also permanently reduce the number of wool follicles in the developing lamb, negatively impacting its lifetime production. Management practices also play a role; increasing the frequency of shearing to twice a year can boost the annual clean wool yield by up to 10% in some breeds.
Converting Raw Fleece to Usable Wool
Grease wool weight is only a preliminary figure because a significant portion of that weight is non-fiber material that must be removed before processing. The difference between the raw weight and the final usable weight is called “shrinkage” or scour loss, measured as the wool yield percentage. This percentage is determined by scouring, an industrial washing process that separates contaminants from the pure fiber.
Weight loss occurs due to the removal of substances naturally present in the fleece. These contaminants include lanolin (the natural grease produced by the sheep), suint (dried sweat salts), dirt, dust, and vegetable matter like burrs and seeds.
The yield percentage varies dramatically depending on the sheep breed and its environment. Fine-wool breeds like Merino naturally produce more lanolin, resulting in a higher scour loss, with yields often around 50% or lower. In contrast, medium-wool breeds like Romney may have a better yield, commonly falling into the 60% to 65% range. For example, a 10-pound raw fleece from a fine-wool sheep with a 50% yield produces only five pounds of clean, usable fiber.