There are a number of plants, such as yellow foxtail (Setaria glauca), needle and thread grass (Stipa comata), foxtail barley (Hordeum jubatum), squirreltail (Sitanion hystrix) and cheatgrass (Bromus tectorum) that may cause mechanical injury to the oral tissues of grazing animals. Of these, yellow foxtail creates significant animal health problems and is commonly found in the Columbia Basin, particularly in poorer hay fields and pasture stands.
Yellow foxtail is a summer annual which germinates when the soil temperatures reach 65 degrees F. The plant grows 1 to 3 feet tall with erect stems that branch at the base. It flowers and produces seed from July through September. The seed head is cylindrical, yellowish, and composed of numerous, tightly packed, mostly single-flowered spikelets. Extending under each spikelet is a tuft of 5 or more fine, wiry bristles that gives it a fuzzy-surfaced appearance which resembles the tail of a fox. The seeds are oval, approximately 1/8 of an inch long, and have sharp awns, or spikelets, that have tiny upwardly directed barbs or points. These bristles easily penetrate flesh, are kept there by the barbs, and can become embedded in the tongue and gums of livestock. Yellow foxtail is native to Eurasia, but is common throughout the western U.S. It is often a serious problem in spring seeded alfalfa and in thin, weak stands of grass hay and pastures.
Relatively small amounts of yellow foxtail in hay and pasture result in rapidly developing, extensive ulceration of the oral tissues of grazing animals, particularly those of horses.
Initial symptoms may be excessive salivation, but in time the awns, or spines, become imbedded in the mucosa, creating ulcers on the tongue and oral tissues lining the mouth. Ulcers average ½ inch in diameter and are surrounded by a white, raised rim. These ulcers, and smaller discolored areas in the tissues, usually contain bristles of yellow foxtail when examined closely. It is also not uncommon for some sharp awns to penetrate the oral tissues, migrate through the tissues away from the site of penetration, and act as a foreign body causing abscesses and draining wounds.