Field peas are grown for livestock feed in northern states from New York west to Oregon, where they are seeded in early spring. In the South they are seeded in the fall for winter pasture and green manure. For harvesting dried peas, fields are mowed, the vines windrowed to dry, then threshed with combines. Straw after threshing, as well as the peas, are nutritious feeds. Some toxic relatives of field peas are the locoweeds.
Some species contain a compound called swainsonine and are toxic to livestock.
Affected animals show nervous system impairment, with symptoms such as dullness and excitement, as well as immune system impairment. Abortion and congenital birth deformities may occur. Locoism affects animal growth, the reproductive system and, probably the most detrimental, the nervous system with the classic symptoms of tremors and nervous activity. These flavonoids induce rhizobial nodulation genes to synthesize Nod factors, which deform root hairs and allow rhizobia to invade the plant through the root. The rhizobia penetrate to the inner cortical plant cells and become enclosed in sacs by plant plasma membranes.