Yew is a shrub, or small tree, which usually grows to a maximum height around 20 feet tall. It is an evergreen, with leaves that look very sharp but are actually soft to the touch. Berries appear on female plants after the flowering period in March, and slowly turn to red in the fall.
Various species can be found throughout the United States and Canada, though they are usually not found in the western Great Plains area. They are usually part of landscapes that are managed. They prefer areas that are extremely humid and have acidic soil, making them more likely to be found in the south and along the coasts.
The entire plant is toxic, both fresh and dried. The most toxic plant component is the leaves during wintertime.
The usual method of poisoning is when clippings from these plants are tossed over pasture fences by unknowing people. Poisoning can also occur when horses escape their pastures and end up in landscapes that contain this plant.
This plant is extremely toxic, with as little as 6-8 ounces of the fresh plant capable of killing an adult horse within 5 minutes. Often horses are found dead with yew leaves still in their mouth.
Alkaloids present in the plant are the cause of poisoning. Symptoms appear rapidly, and unfortunately, usually the horse is found dead in the pasture without any prior signs being noticed.
The cause of death is the inability of the heart muscles to depolarize, which is caused by the alkaloids.
If the horse is seen very soon after consuming the plant, the following signs may be noticed:
If the horse is found quickly enough, supportive cardiac and vascular therapy may be beneficial, as well as detoxification. Atropine may be beneficial to correct the slow heartbeat brought on by poisoning.