University of Wyoming

Trace mineral concentrations in common Wyoming plants on sheep winter range



As of January 2018, Wyoming has a breeding sheep inventory of approximately 260,000 head. The majority of these

ewes occur on ranching enterprises relying on extensive rangelands. A major problem in this production environment is

the mismatch between available forage quality and sheep production stages, specifically during the physiologically

demanding periods of breeding and pregnancy when the nutritional composition of grazing diets is at it’s lowest

nutritive value. While more obvious aspects of this problem have been quantified on sheep winter range such macro

nutrients including energy and crude protein, very little information about trace mineral composition of grass and

browse species on winter range has been developed for sheep producers. For sheep operations in the western United

States that rely on naturally grown rangeland forage as their primary feed source, this is problematic because clinical or

subclinical trace mineral deficiencies that limit animal productivity may manifest themselves. Such issues related to

trace mineral deficiencies that could arise include a broad spectrum of problems related to essential perform essential

functions including structural, physiological, catalytic, and regulatory roles (Suttle, 2010). Finally, because forage trace

mineral concentrations are highly variable across rangelands due to the strong influence of soil geochemistry and plant

stage of maturity, more information is necessary to deal with this complex issue (Mathis and Sawyer, 2004; Smith et

al.,2014; Jones and Tracy, 2015).Many range sheep operators do not provide a free choice mineral while on winter range

which could predispose ewes to clinical and subclinical trace mineral deficiencies. While the reasons for not providing a

trace mineral supplement vary, among Wyoming range flocks many deficiencies and subclinical deficiencies go

undiagnosed and may not always be solely attributed to trace mineral deficiencies. By characterizing the trace mineral

composition of consumed rangeland plants, we will be able to build trace mineral maps for Wyoming and a calculator

tool to assist producers in making supplementation decisions and to guide feed manufacturers in formulating regionallyor

ranch- specific mineral packages. A similar study funded by NSIIC in 2016 was recently published in the scientific

journal ‘The Professional Animal Scientist’ and reported that 33% of Montana (MT) ranches were not providing a

complete mineral, and that 19 and 23% were deficient or marginally deficient in selenium (Se) and 10 and 57% were

deficient or marginally deficient in zinc (Zn). Participating ranches in the MT study anecdotally reported improvements

in animal health and lamb and wool growth when trace mineral supplementation was offered to the flock. The ability to

engage Wyoming sheep producers in this type of field research not only answers important production questions, but

more importantly, has the potential to reduce production losses due to trace mineral deficiencies. Experience from the

Montana study demonstrated the value of engaging producers with field research as a means of understanding what is

happening at an operational level so that better management decisions are made. Furthermore, conducting translational

research of this nature allows sheep extension personnel to work with mineral manufacturers to provide a more tailored

product for range-sheep producers.