38. COMMON ST. JOHNSWORT, KLAMATH WEED

Hypericum perforatum

(St. Johnswort family)

TOXICITY RATING: Low to moderate.

ANIMALS AFFECTED: Cattle, sheep, goats, horses, and swine.

DANGEROUS PARTS OF PLANT: All parts.

CLASS OF SIGNS: Sunburn, skin slough, eye irritation.

PLANT DESCRIPTION: This perennial herb (fig. 38) grows 1 to 11/2 feet 1/2 to 1 inch long and flat-topped clusters of golden yellow flowers 3/4 to 1 inch broad which bloom from midsummer to late fall. The five petals often have distinctive black dots around their edges (fig. 38A) and the leaves may have similar dots (fig. 38B). St. Johnswort commonly grows in droughty, poor, or over-grazed meadows, pastures, fields, and waste areas, usually on dry, gravelly, or sandy soils in full sunshine. Other species of Hypericum occur in Indiana, some as garden plants. Although the evidence of their toxicity is not as clear, it may be prudent to avoid them, too.

SIGNS: The toxin in St. Johnswort is called hypericin. When animals ingest the plant, the hypericin is absorbed from the intestinal tract and goes into the circulation. Hypericin is photodynamic, able to convert sunlight into energy (primarily heat), causing cellular damage and sunburn (which can be severe). Cattle and sheep are the most sensitive to this toxin, but swine and horses may also be affected.

St. Johnswort is not palatable and is eaten only when better food is unavailable. Animals must consume the plants for 4 to 5 days or more before clinical signs are noted. The affected skin first becomes swollen and tender, then reddened. This occurs primarily on the lightly pigmented areas (pink or white skin), and on the areas of the body that receive more sunlight (head, neck, back). The skin can be burned to the point where large areas of skin peel off. This is extremely painful, and predisposes the animal to infection. Affected animals are reluctant to have the areas examined, and may act abnormally and not want to eat due to the discomfort. Occasionally the eyes will be affected, causing redness and inflammation of the eyelids and the eye itself. These animals may not be able to see.

There are many plants that can cause sunburn either by contact or ingestion. In addition to St. Johnswort, some types of clover, vetches and buckwheat (Fagopyrum) have caused sunburn and skin scald in animals.

FIRST AID: The first steps are to prevent further consumption of the plant and to get the animals into the shade or a barn. Emergency evacuation of the gastrointestinal tract is not required since the toxin takes several days to build up in the body and cause signs. If the sunburn is mild, conservative treatment and supportive care is all that is required. Animals will resent handling, and horses will not be able to be ridden for at least 1 to 2 weeks. Keep animals in the shade, consider turning them out at night only. For more severely affected animals, including animals whose eyes are affected, or where the skin is blistered or sloughing, a veterinarian needs to be contacted, and antibiotics and anti-inflammatory medications provided.

SAFETY IN PREPARED FEEDS: The toxin in St. Johnswort remains active even when the plants are dry, therefore hay or processed feeds will still be toxic and should not be fed. However, if the hay needs to be fed under extreme circumstances, keep all animals out of direct sunlight for up to one week after the contaminated feed is no longer being used.

PREVENTION: Animals will voluntarily avoid St. Johnswort if more nutritious and palatable forage is made available. If the pasture contains large stands of this plant, it may be best to mow, spray, or re-seed to improve the pasture quality and eliminate potential problems. If the plants are to be sprayed, keep animals off the pasture until the plants are completely dead, since herbicide treatment often increases plant palatability.