Toxic Principle

The toxin in hairy vetch responsible for the symptoms is not known. The toxin appears to cause an immune-mediated disease as prior exposure or sensitization is necesary for the disease to develop. Animals grazing the green vetch develop a severe granulomatous disease affecting many organs. The seeds of hairy vetch when eaten in quantity by cattle and horses cause nervous signs and death. The seeds of Vicia sativa have been reported to contain cyanide.

Description

An annual with stems 4-6 feet in length, with hairy stems and leaves. The leaves have 10-20 leaflets up to 1 inch in length which are narrow and lance-shaped. Tendrils at the end of the leaves are well developed. Flowers are purple to redin color, 20-60 per spike, all on one side of the flower stalk. Pods are about 1 inch in length containing several hard seeds.

Gastrointestinal

Diarrhea, poor appetite.

Cardiovascular system

Sudden death may be associated with cyanide in the seeds.

Nervous System

Abnormal behavior, excessive bellowing, difficulty in standing, convulsions and death from eating quantities of the hairy vetch seed.

Integumentary System

Initially animals have welts on the skin, with hair loss, thickening of the skin, itching and rubbing of the affected areas, and peeling of the skin around the nose and eyes. Lymph nodes are swollen and ventral edema is common.

Diagnosis

Lymphocytosis and hyperproteinemia are common features of hairy vetch poisoning. Microscopically, the skin, heart, liver and other organs have cellular infiltrates of lymphocytes, monocytes, and multinucleated giant cells typical of an immune-mediated granulomatous reaction. Mortality is usually high.