St. Johnswort grows along roadsides, in meadows, pastures, range lands, and waste places. In the Pacific Coast States, it may reach a height of 5 feet; in other areas, it grows 1 to 3 feet tall. It is a perennial.
St. Johnswort is a smooth-branched erect plant. Leaves are covered with clear small dots that contain the toxic substances. Five-petaled flowers grow in clusters; they are orange-yellow with occasional black dots along the edges. After maturity, flowers wilt and the entire plant turns brown.

St. Johnswort or Klamath weed, is a range plant that makes white-skinned animals alergic to sunlight. Animals that eat this plant and then are exposed to direct sunshine develope a severe sunburn in white areas of the skin.

According to legend, the plant is called St. Johnswort because it blooms on June 24th, or St. John the Baptist day. Other common names are goatweed, Tipton weed, Eola weed, amber, and rosin rose.
Young cattle and sheep are most often affected, but almost all white-skinned cattle, sheep, and horses react to eating the plant. Recently sheared sheep are especially susceptible. Althought it seldom kills, it causes severe economic losses.

St. Jonswort is dangerous at all stages of growth. Young tender shoots may attract animals in the spring. Normally, cattle and sheep will not eat the mature plant if they have other forage. Hay containing the plant can cause poisoning in the winter.
The poisonous substances in it are hypericin and hypericum red.
Other poisonous plants-horsebrush and spring parsley-also produce reactions to sunshine.

Where and When It Grows
St. Johnswort is an aggressive plant. It grows in old meadows, on pastures, along roadsides, on range land, and in waste areas. It usually is found on dry, gravelly, or sandy soils in full sunshine. It may grow in dense patches or mixed among other plants. Plants start growth in early spring.

How It Affects Livestock

St. Johnswort was the first plant known to cause photosensitization. When an animal eats the green plant, the toxic substances pass through the liver without causing damage. On reaching the skin, hypericin sensitizes white areas. The affected animal then becomes burned when exposed to direct sunlight.
White-skinned cattle are more susceptible to the plant poisoning than white-skinned sheep.
Cattle are poisoned by it if they eat an amount equal to 1 percent of their body weight-and are then exposed to direct sunshine for 2 to 5 days.

Death may occur within 3 days after cattle eat green plants equal to 5 pecent of their body weight.
Before sheep show even slight signs of poisoning, they must eat enough to equal 5 percent of their body weight. An amount of the plant equal to 4 percent of the body weight produces no effect in sheep, experiments have shown.

On the range, signs of poisoning usually appear 2 to 21 days after animals have had access to the plant.
Dark-colored animals have enough skin pigment to screen out undesirable sun rays, so they are not affected by the toxic substances in the plant.

Signs of poisoning

1. Restlessness
2. Scratching head with hind legs and rubbing head against solid objects.
3. Crouching
4. Diarrhea
5. Rapid pulse, increased temperature
6. Sunburn of white-skin areas
7. Blisters on 2nd day
8. Matted wool or hair
9. Swollen eyelids, clouded eyes
10. Convulsions



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