There are many plants that are poisonous to equines. The species vary depending on location, climate and grazing conditions. In many cases entire genuses are poisonous to equines and include many species spread over several continents. Plants can cause reactions ranging from laminitis

Laminitis

Laminitis is a disease that affects the feet of ungulates. It is best known in horses and cattle. Symptoms include lameness, and increased temperature in the hooves...

 (found in horses bedded on shavings from black walnut

Black Walnut

Juglans nigra, the Eastern Black walnut, is a species of flowering tree in the hickory family, Juglandaceae, that is native to eastern North America. It grows mostly in riparian zones, from southern Ontario, west to southeast South Dakota, south to Georgia, northern Florida and southwest to central...

 trees), anemia

Anemia

Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

, kidney disease and kidney failure (from eating the wilted leaves of red maple

Red Maple

Acer rubrum , is one of the most common and widespread deciduous trees of eastern North America. It ranges from the Lake of the Woods on the border between Ontario and Minnesota, east to Newfoundland, south to near Miami, Florida, and southwest to east Texas...

s), to cyanide

Cyanide

A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

 poisoning (from the ingestion of plant matter from members of the Prunus

Prunus

Prunus is a genus of trees and shrubs, which includes the plums, cherries, peaches, apricots and almonds. There are around 430 species spread throughout the northern temperate regions of the globe. Many members of the genus are widely cultivated for fruit and ornament.-Botany:Members of the genus...

genus) and other symptoms. Members of the Prunus genus have also been theorized to be at fault for Mare Reproductive Loss Syndrome

Mare Reproductive Loss Syndrome

Mare Reproductive Loss Syndrome has been diagnosed in mares of all breeds and ages. It was initially observed in Kentucky in a three week period around the first of May, 2001, when about 20% to 30% of Kentucky's pregnant mares suffered abortions...

.