Could you recommend some good references with information about plants that are toxic to livestock, particularly to horses?
There are a number of resources which list plants that are toxic to animals, and specifically to horses. As you check the lists, keep in mind that just because a plant is not on the toxic list, one cannot assume it is non-toxic.
Here are links to some useful lists:
ASPCA Lists of Plants:
Cornell University Department of Animal Science: Plants Poisonous to Livestock (search by affected animal species)
Selected Poisonous Plants of the Pacific Northwest toxic to livestock, from Washington State University
Dr. Duke’s Phytochemical and Ethnobotanical Databases, from
Agricultural Research Service: try searching by plant name. Highly technical, but shows what the active chemical properties are in various plants.
Reprint from Trailblazers magazine
Ten most poisonous plants affecting horses, from the editors of Equus magazine
The Miller Library also has the booklet entitled Commonly Cultivated and Native Oregon Plants Toxic to Domesticated Animals by La Rea Dennis et al., Pacific Western Research, 1990. It is organized by plant family, not by affected animals.