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UW sheep specialist tasked with supplement research

by Wyoming Livestock Roundup

University of Wyoming (UW) Assistant Professor and Extension Sheep Specialist Dr. Whit Stewart was recently asked by a scientific journal to contribute to the findings of sheep supplementation. The review paper he submitted in response is a summary of all international research, along with some of UW’s own research data on mineral supplementation for sheep.     

“It was prestigious to be asked to be an authoritative resource in this certain field,” says Stewart.   

Supplementing sheep is a much more difficult task in the western U.S., compared to the Midwest and Southeast. In the West, sheep graze diverse landscapes with various soil types and plant communities. Whereas in the Midwest and Southeast, sheep have simple diets with a few ingredients, so it’s easier in those circumstances to create beneficial mineral programs.    

Soil mineral, diet preferences and supplementation are all covered in Stewart’s review.  

Soil assessments     

If soil is measured only for mineral content, producers are left with many unknowns. Stewart’s review states understanding mineral content of the soil may not always directly reflect what is absorbed by the plant and is available for livestock use. This can make it difficult when assessing what nutrients sheep are directly consuming.  

A good place for producers to start when looking at their soil, is to see if there are any antagonistic minerals which could affect sheep diet.    

“High molybdenum levels in soil, generally speaking, will reduce copper consumption,” Stewart explained. “The soil assessments help with understanding those broad relationships that cancel or reduce other minerals.”  

While Stewart notes soil assessments can be beneficial, they may not be as informative as a complete forage analysis.  

Dietary preference     

Sheep have more flexibility in their dietary preference when compared to other livestock. In fact, sheep are much better at utilizing broadleaf forbs and shrubs, also known as browse, than cattle. This is an especially important forage resource in winter months, as research has shown grazing has the ability to provide a compete mineral package for sheep, Stewart noted.   

“If producers in Wyoming are grazing a winter range that is a restored pasture of crested wheatgrass or a cool season grass, generally speaking, the forage will have less available minerals later in the season rather than a pasture that is super diverse in its plant species,” said Stewart.  

Although many producers worry about the animal’s low copper tolerance, range diets seem to be tailored for sheep.   

“Sheep actually do have a very small copper requirement which is fulfilled in everyday forage,” Stewart explained. “Sagebrush, salt sage and other small shrub species have the ideal amounts of copper for sheep and their grazing diets.”  

Supplementation in different scenarios    

Mineral supplementation can be very easy if sheep are in a drylot, eating one or two main ingredients like alfalfa or are supplemented with grain. However, grazing sheep in large and diverse pastures makes providing supplement complicated.    

“We recommend keeping a mineral in front of the herd, but sheep will over-consume that mineral,” Stewart shared. “We preach it’s important to keep a mineral out during more demanding physiological times, for example, breeding, pregnancy and lactation. It is most important to provide mineral during those most demanding times.” 

Building a mineral program    

The first step to building a mineral program, according to Stewart, is analyzing forages and investing in forage tests every few years to see what the grass or harvested feed looks like in terms of mineral content.   

“Once producers have a picture of what is provided to the sheep in their basal diet, what’s provided out in pasture and what they are picking up themselves, then they can structure their mineral program,” he explained. “I can say with some certainty the standard commercial sheep mineral supplement will meet those needs overall with some exceptions. However, for more mineral specific supplementation, producers should look closely into the diets.”    

“When producers realize what’s in the basal feed ingredients, they can make up for the shortfall with a supplementation package,” says Stewart.    

Cameron Magee is an intern for the Wyoming Livestock Roundup. Send comments on this article to

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