Invasive weeds intrude on millions of acres across the Western United States, pushing out native plants and devastating ecosystems. Most of these plants were introduced from Europe and Asia, where they are a small part of natural systems. However, in the United States, the vegetation dynamics and grazing regimes have contributed to their explosive spread.

Cattle and sheep will consume moderate amounts of virtually all plants, including invasive or noxious weeds, during one part or another of their growing cycle. Karen Launchbaugh, a BEHAVE collaborator and Department Head of the Department of Rangeland Ecology and Management at the University of Idaho, is working with other researchers to study the relationships between animal condition and circumstance and how these factors influence consumption of weedy plants. This research has made enormous progress toward understanding how to reduce the abundance of noxious weeds using grazing animals.

Research in 2003 focused on how age and body condition of goats affect consumption of invasive juniper species, plants that contain terpenes. Initial results confirm that the body condition of grazing animals dramatically affects the amount of a juniper a goat will eat. Goats in low body condition ate four to five times more juniper than goats in high body condition. They also found that young animals ate significantly more juniper than mature animals regardless of body condition. Young animals are apparently more willing than older animals to accept novel foods and foods that previously made them ill.

Research in 2005 focused on how livestock age and body condition affect their use of chemically defended plants. We specifically addressed how age and body condition influences the kinetics and elimination of monoterpenes from the bloodstream of goats. Body condition influenced the concentration and elimination of 4 monoterpenes found in juniper. We found that animals in low body condition are more willing to consume plants containing monoterpenes, they may not be as well equipped to detoxify them. This research is important because many rangeland plants contain monoterpenes, including sagebrush and juniper. Additionally, age or body condition of livestock can be managed to improve the effectiveness of prescribed grazing practices for vegetation management.

Efforts to increase the consumption of invasive plants by livestock continues with a project to determine the nutritive value of 8 species of weeds common in the Northwest. A clipping study was undertaken this past spring in which plants were collected in the rosette, bolt, flower, and seedset stages to be analyzed for NDF, ADF, crude protein, and possibly soluble carbohydrates. This information has been requested by those in the vegetation management industry and promises to be a useful tool in selecting the best class of animal for a prescription grazing project. Species being anlyzed are:

1. Dalmation toadflax (Linaria dalmatica)
2. Meadow hawkweed (Hieracium pratense)
3. Houndstongue (Cynoglossum officinale)
4. Rush Skeletonweed (Chondrilla juncea)
5. Sulfur cinquefoil (Potentilla recta)
6. Tansy ragwort (Senecio jacobaea)
7. Whitetop (Lepidium latifolium)
8. Yellow starthistle (Centaurea solstitialis)