Prominent in extreme western U.S., has also spread throughout other regions. Predominant in uncultivated fields, roadsides and waste areas.
The plant is not usually eaten unless other forage is unavailable, or when incorporated into hay. Poisonings occur at ingestions of 50%- 200% of the animal's body weight over a 60 to 90 day period of grazing. Clinical signs have been referred to as "chewing disease", where horses chew but are unable to obtain food or swallow. Signs seen include a grinning appearance, open mouth with protruding, lolling tongue, yawning, head tossing, central nervous system depression, lost interest in food, difficulty breathing due to inhalation of food, submerging the head in water in an attempt to drink. Death can occur due to lack of eating and drinking, leading to dehydration and malnutrition.
Toxic to Horses