Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Wildland Resources

Department name when degree awarded

Forest, Range, and Wildlife Sciences

Committee Chair(s)

Frederick D. Provenza


Frederick D. Provenza


Michael H. Ralphs


Jeffery O. Hall


Juan J. Villalba


Kenneth C. Olson


The sagebrush steppe is one of the most extensive vegetation types in the western US and an important habitat for wild and domestic herbivores. When sagebrush dominates, however, forage and habitat quality decline. Although sagebrush is nutritious, its forage value is reduced by terpenes. A better understanding of how terpenes limit intake is vital for increasing consumption of sagebrush and for enhancing and maintaining biodiversity in the sagebrush-steppe.

To better understand how terpenes in sagebrush limit intake, we studied feeding behavior of sheep in the field, influence of sagebrush monoterpenes on regulation of intake in pens, and the feeding behavior of lambs in relation to the kinetics of camphor, 1,8-cineole, and p-cymene dosed intravenously and intraruminally.

In field studies, supplemented ewes utilized more sagebrush than unsupplemented ewes. In pen studies, food intake and dietary concentrations of monoterpenes were inversely related. Lambs regulated feeding bout frequencies to minimize the toxic effects of monoterpenes.

We proposed four complementary hypotheses to account for physiological mechanisms by which monoterpenes influence feeding behavior: 1) monoterpenes disturb acid-base balance, 2) monoterpenes cause satiation, 3) monoterpenes induce elimination pathways, and 4) rumen microbes adapt to monoterpenes. The first two addressed how monoterpenes limit intake and the last two addressed adaptation to monoterpenes.

There was no induction of elimination pathways or disturbance of acid-base balance. Camphor, 1,8-cineole, and p-cymene dosed individually and in a cocktail affected feeding behavior and limited food intake by lambs. Feeding time did not change with repeated intravenous dosing with camphor, increased slightly with intravenous dosing with p-cymene and the terpene cocktail, but declined with intravenous dosing with 1,8-cineole. Lambs increased feeding time and food intake with repeated rumen dosing with camphor, 1,8-cineole, and the cocktail. Feeding time and food intake did not change with rumen dosing with p-cymene.

Exposure to a terpene-containing diet led to rumen microbial adaptation, while kinetic rates remained unchanged. Satiation, elimination rates, and rumen microbe adaptation influence feeding time and food intake of lambs. Timing of grazing, supplements, stock density, and detoxification of sagebrush monoterpenes influence feeding behavior of sheep, with significant implications for biodiversity of sagebrush-grassland ecosystems.