Dandelions are not known to be toxic to horses. However, false dandelions are thought to cause stringhalt in horses if too many are consumed. Stringhalt is a spasmodic contraction of the lateral flexor tendons in the hind legs, which presents as a sudden flexion of one or both hind legs.
False dandelion causes the breakdown of the myelin sheath that covers nerves, causing damage and muscle atrophy.
Horses that are less severely affected may show signs of incoordination or dragging of the hind hooves. Horses chronically consuming false dandelions may also experience muscle atrophy.
Dandelions are highly efficient as a medicinal plant- the roots, leaves, and flowers can all be fed to horses for beneficial effects. Leaves can be fed fresh or dried and are most effective for increasing urination and flushing the body. Fresh leaves are best fed in handfuls as a snack, and no more than 1.7 ounces for a 1100 lb horse or a teaspoon of dried leaves per 20 lbs of weight. Leaves are best harvested in early spring when they are least bitter and tenderer.
Dandelions are a great treatment for horses with stomach upset (not for ulcers- see below) caused by intestinal blockage as dandelions increase bile and encourage movement in the digestive tract. They also encourage urination, and are a very effective detoxifying healing agent after an illness. More generally, dandelions can be fed as a general source of key nutrients that are often lacking from a hay-only diet.