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Sheep nutrition affects fiber capability

by Wyoming Livestock Roundup

“When most people think sheep, they think meat,” said Small Ruminant Nutritionist Nancy Irlbeck of Colorado State University, “but my primary emphasis is on wool production.”

During a Sept. 10 webinar, Irlbeck noted that nutrition can be utilized to increase wool production in sheep.

“When we look for good fiber, the literature tells us we want a low micron count and heavy fleece weight,” she explains, “but is it realistic?”

Not only is it realistic, Irlbeck noted that through proper nutrition, wool production can be optimized. 

Fiber factors

When looking at wool fiber production, Irlbeck marked genetics and the environment as the two primary factors that contribute to wool quality. 

“Using electron microscopy, we get a perception of what we can do looking at different wools,” she explained. 

Looking under the microscope, lamb’s first wool shows a sharp-pointed tip on each fiber, because they have never been sheared. The wool is finer and popular with hand spinners, she noted. 

Conversely, sheared wools have a blunt end, making it less desireable.

Microscopically analyzing wool also reveals nutritional impacts. 

“With a poor diet, the sheep have very thin fibers,” Irlbeck explains. “While some may think that thin fibers are good, I would not advise underfeeding. Thin fibers see an increase in fractures and breaks.”

On the other hand, overfeeding results in coarser wools.

“Overdoing it and treating the animals so they become fat is almost as bad as underfeeding,” she explained.

Additionally, stressful periods in the sheep’s life can also result in stress breaks in the wool. 

Primary follicles

In looking at achieving maximum wool production, developing the highest number of follicles possible is important.

“The follicles for fiber production are actually an extension of the skin,” explained Irlbeck. “The wool is actually part of the animal’s skin.”

There are two types of follicles – primary and secondary – that are integral in wool production.

“The primary follicles are associated with the sweat glands, a muscle gland and the sebaceous gland, which produces lanolin,” she continued. “The number of primary follicles that a lamb can form is determined genetically.”

Genetic selection can increase the number of primary follicles available, but Irlbeck also cautioned against single trait selection.

“There are many people who have tried to breed genetically for finer and finer wools, but there is always concern with the consistent selection of one trait,” Irlbeck mentioned. “With genetics, we can only do so much.”

Environmental influence

However, the environment controls the total number of follicles formed.

“The secondary follicle only has the sebaceous gland with it,” Irlbeck said, noting that the follicles are formed based on the quality of nutrition prior to birth.

During the third trimester, the majority of fetal growth occurs. 

“The third trimester is where our sheep need the most groceries,” she commented. “The last trimester is when we have the greatest demand for nutrition.”

Irlbeck explained that as the lamb grows, the ewe’s rumen has a smaller capacity, meaning she is unable to eat as much, but her nutritional requirements remain high.

“Primary follicle development occurs from day 60 to day 90 of gestation,” continued Irlbeck, noting that primary follicle development falls in the second trimester of development. “Secondary follicle development is from day 90 to birth.”

“If producers are feeding the animals according to physiological status and feed the most nutrients in the third trimester, they will have the greatest amount of secondary follicles production,” Irlbeck said.

The secondary follicles, she added, are those that add density to fleeces and increases profits. 

 To drive the point home, Irlbeck stated, “When we have ewes that have received good nutrition, the number of primary follicles doesn’t change, but the number of secondary follicles increases because we fed them right.”


“It is rare for a pasture sheep to reach their maximum genetic potential for wool production if their only source of nutrition is in the grazing forage,” Irlbeck noted.

Nutritional impacts, she continued, are greatest from pre-weaning when the lamb is still nursing, late pregnancy, lactation and post-weaning.

If ewes aren’t fed properly during pregnancy, the results are irreversible.

“If ewes have poor nutrition during pregnancy and early lactation, it will impose a permanent limitation for wool production,” she emphasized. “We can’t go back and fix it no matter what.”

The webinar was hosted by Colorado State University and sponsored by the American Sheep Industry Association’s Rebuild the Sheep Inventory Committee. Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at

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