Date of Award:

5-2026

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Chad M. Page (Major Professor) Kara J. Thornton (Co-Advisor)

Committee

Chad M. Page

Committee

Kara J. Thornton

Committee

Katherine M. Kennedy

Committee

Chad L. Gasser

Committee

Kerry A. Rood

Abstract

Sheep producers in the Intermountain West region of the US rely on productive rangeland ecosystems that vary widely in forage composition and nutrient availability. As such, supplementation is often necessary to offset dietary deficiencies. Soils and forages grown on rangelands are known to be highly variable in mineral content. Even so, a third to half of the producers in the Intermountain West choose not to provide a complete mineral supplement. Rangeland environments are often characterized by rugged geographical features that make optimal supplement placement difficult. New advances in technology have allowed us to measure individual animal intake on rangelands via feed bunks that can track electronic identification tags in animals’ ears. Little information exists on how mineral supplementation influences performance, forage selection and rangeland utilization of grazing ewes. The research presented in this dissertation is a two-year study that examined the differences between ewes who were able to receive a free-choice mineral supplement and ewes who were not allowed to consume the supplement while grazing. Use of the mineral supplement was below what was expected in both years. In both years, mineral supplementation had minimal effects on weight gain and mineral status. Mineral content of the blood and liver was similar for all minerals measured. Most blood and liver mineral concentrations increased during the grazing season, independent of access to the supplement. All minerals were also within ranges that indicate the animals were not in a state of deficiency or toxicity. Forage selection was not affected by access to a mineral supplement, with most ewes selecting flowering leafy forage. Utilization of rangelands was influenced by factors such as terrain ruggedness and elevation, compared to access to the mineral supplement. Ewes strongly avoided areas that had abrupt changes in elevation. Ewes preferred to graze on eastern and southern slopes. The findings of this study indicate that rangelands with diverse plant populations provide many of the dietary requirements of grazing ewes. Producers may be able to save money by supplementing white salt during the grazing season and providing a complete mineral supplement during more nutrient-demanding stages of production, such as lambing, weaning and breeding.

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Creative Commons Attribution-Noncommercial 4.0 License
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