Oregon State University Extension Service

Plants causing liver disease and sunlight sensitivity in pastures

Plants causing liver disease and photosensitization (sensitivity to sunlight) are often grouped together. Photosensitization is often, but not always, a secondary symptom of liver disease caused by poisonous plants.

As chlorophyll breaks down, it becomes phylloerythrin, a phototoxic compound. In healthy animals, the liver filters phylloerythrin from the blood, preventing any damage. If the liver is compromised by toxins, it is unable to remove the compound from the blood, and photosensitization occurs.

Some plants contain compounds that, once absorbed into the bloodstream, react to UV exposure without any effect on the liver. Photosensitization resembles severe sunburn. Plants from a variety of families can impact liver health or cause related nutrient deficiencies. Photosensitization symptoms are most pronounced on white-skinned animals or on white-skinned areas, around the face and near the hooves.

Common pasture plants affecting the liver and blood and/or causing photosensitization:

Onion

  • Photo: onion

Allium spp.

Identification: Narrow, linear, fleshy leaves; round stem; single bulb. White flowers in umbel borne on leafless flower stalk. Strong onion odor.

Habitat: Meadows, pastures.

Animals affected: Cattle are most susceptible, horses and dogs semi-susceptible; sheep and goats most resistant.

Toxin family: Alkaloids damage red blood cell metabolism.

Other: Most poisonings are due to feeding animals cull domestic onions — rarely from wild onions. The first sign of toxicity is generally dark red-brown urine, weak pulse and onion breath. Alliums cause milk to taste like onion. The onion flavor will disappear if the animal is cut off from eating onions for 24 hours.

Flixweed/tansy mustard

  • Flixweed

  • Flixweed

Descuriania sophia

Identification: Up to 2-foot-tall winter annual/biennial. Pubescent, alternate leaves two to three times pinnately compound, with linear segments. Flowers a raceme of tiny yellow flowers and fruit a long, narrow pod, maturing from the bottom of the plant up.

Habitat: Waste areas, roadsides and disturbed sites.

Animals affected: Cattle.

Toxin family: Unknown.

Other: Causes sporadic poisoning presenting as blindness and the loss of use of tongue and throat, or as liver disease and photosensitization.

Horsetail and scouring rush

  • Horsetail

  • Horsetail & Scouring Rush

  • Horsetail & Scouring Rush

Equisetum spp.

Identification: Perennial with dimorphic stems. Vegetative stem has whorls of fine, green, jointed branches. Reproductive stem is flesh colored, unbranched, with a single cone at its tip.

Habitat: moist to wet forests, meadows, swamps, roadsides and areas with high water tables.

Animals affected: Primarily horses.

Toxin family: Thiaminase; causes Vitamin B deficiency.

Other: Symptoms include weight loss, diarrhea and weakness, leading to immobility and death. No loss of appetite. All plant parts are poisonous. Becomes increasingly toxic when dry, in hay.

St. Johnswort

  • St. Johnswort flowers

  • St. Johnswort leaf

Hypericum perferatum

Identification: 1- to 3-foot-tall perennial. Erect stems, rust colored at base. Opposite, oblong leaves covered with transparent dots. Bright yellow flowers in cymes, often with black dots on petal edges.

Habitat: Pastures, rangeland and open timber. Prefers well- drained soil.

Animals affected: Cattle, sheep and horses.

Toxin family: Hypericin (a photoreactive pigment) from the glandular dots on leaves is absorbed after ingestion, causing photosensitivity (skin cell death).Pprimarily affects white-skinned animals; death rarely occurs.

Other: Causes blisters around the mouth, eyes, ears, nose and feet when exposed to light. Young plants palatable; mature plants not as much. Toxic at all growth stages. Remains toxic in hay.

Western bracken fern

  • Western bracken fern

  • Western bracken fern

  • Western Bracken Fern

Pteridium aquilinum

Identification: Perennial solitary ferns up to 3 meters tall. Creeping rhizomes, leather fronds and densely hairy on the underside. Brown spores on the underside of frond segments. New growth emerges as fiddlenecks.

Habitat: Open woods, roadsides and burned areas. Prefers neutral to acidic soil.

Animals affected: Primarily horses, but also cows and sheep.

Toxin family: Thiaminase, ptaquiloside.

Other: Thiaminase causes thiamin deficiency in horses and pigs. Animals must eat large quantities, and the deficiency is characterized by central nervous system depression. Ptaquiloside is a carcinogenic and bone marrow depressant. Norsesquiterpene glycoside affects cows and sometimes sheep. Newly emerging fiddleheads are especially toxic and palatable, but animals must eat their weight over several months for disease to develop. Consumption over long periods will cause carcinogenic tumors in the bladder and other parts of the digestive tract. Bracken fern can also cause retinal degeneration and blindness in sheep. Toxins remain in hay and silage. Not highly palatable. All parts are poisonous, the rootstock especially.

False lupine

  • yellow flower on short pealike plant

    False lupine

  • False Lupine flowers

Thermopsis rhombifolia

Identification: Erect, rhizomatous perennial. Alternate leaves are broadly elliptic and trifoliate (unlike lupine, with five or more leaflets). Flowers are yellow and pealike and grow in dense terminal racemes up to 4 inches long. Seedpods are densely haired and curved.

Habitat: Roadsides, pastures and rangeland.

Animals affected: Cattle.

Toxin family: Quinolizidine alkaloids cause muscle degeneration.

Other: Animals that have eaten false lupine show a reluctance to move and muscle tremors if forced to move. Not palatable.

Puncture vine

  • Puncture vine

  • Puncture vine

  • Puncture vine fruit

Tribulus terrestris

Identification: Prostrate, pubescent annual. Pinnately compound opposite leaves with oblong leaflets. Solitary yellow flowers in leaf axils. Fruit is a small, spiny capsule.

Habitat: Waste areas and roadsides.

Animals affected: All livestock.

Toxin family: Steroidal sapogenins and physical injury.

Other: Causes insoluble crystalloid substance in bile ducts, blocking the biliary system and causing photosensitivity. Can also cause neurological symptoms and incomplete paralysis. Burrs are injurious to livestock and humans.

Cowcockle

Vaccaria pyramidata

Identification: 1- to 3-foot-tall annual with many branching stems. Leaves are opposite, lance-shaped and clasp the stem. Flowers occur singly at stem ends and are bright pink.

Habitat: Cultivated fields, roadsides, waste areas.

Animals affected: Most livestock.

Toxin family: Saponin.

Other: Can cause liver degeneration and death if eaten in large quantities. Seeds are especially poisonous to livestock

Cocklebur

  • Cocklebur

  • Cocklebur

Xanthium strumarium

Identification: 4- to 5-foot-tall bushy annual. Large, triangular, rough, glandular leaves. Flowers produced in leaf axils. Blooms in summer. Female flowers become burs with hooked bristles.

Habitat: Cultivated fields, pastures, barnyards and especially sandy soils. Seeds germinate quickly with receding water.

Animals affected: All livestock.

Toxin family: Sulfated glycoside (Carboxyactractyloside) causing liver necrosis.

Other: Death occurs rapidly. Seedlings and seeds are toxic, but toxins are not present in mature plants. Seeds are rarely eaten, as they are contained in a bur. Toxicity remains in hay and silage. Burs also cause economic damage to wool producers.

Sheep in dry pasture
Source URL: https://extension.oregonstate.edu/gallery/plants-causing-liver-disease-sunlight-sensitivity-pastures