Merck Manual

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Substances that can Cause Liver Injury in Horses

Substances that can Cause Liver Injury in Horses

Substance

Possible Sources

Signs

Treatment and Prevention

Iron

Inappropriate iron supplementation, forages high in iron, injectable iron, and leaching of iron into water or feed.

Foals: hepatic encephalopathy, death.

Adults: weight loss, jaundice, depression.

Treatment includes fluids and nutritional supplements. Outlook is usually poor,

Fungal toxins (mycotoxins), especially -Fusarium

Feed or bedding contaminated with mold toxins, especially corn.

Drowsiness, difficulty breathing, jaundice, neurologic signs, blindness, collapse, death.

No treatment available; screen grain to remove broken or small grains.

Blue-green algae

Contamination of drinking water by blue-green algae.

Death may occur within a few hours and may be preceded by coma, muscle tremors, diarrhea, and difficulty breathing; horses that survive may have light sensitivity.

Replacement of contaminated water with large amounts of fresh water; affected horses should be kept out of direct sunlight. Techniques to prevent the growth of algae in water sources.

Pyrrolizidine alkaloid toxicity (compound found in many plant species, for example, ragwort, groundsel, fiddleneck)

Plants are normally avoided during grazing but may be eaten during drought or may be found in contaminated hay.

Exposure is usually longterm; causes loss of condition and appetite, constipation or diarrhea, jaundice; exercise intolerance, light sensitivity, and hepatic encephalopathy; can be fatal.

Rations high in carbohydrates and low in protein; protein should be high in branch-chain amino acids. Prevention via herbicide control of offending plants.

Kleingrass (Panicum coloratum)—toxin is sapogenin

Found in southwestern United States from late spring to early fall; young growing plants contain highest toxin concentration.

Jaundice, light sensitivity, intermittent colic and fever, weight loss, and hepatic encephalopathy. Light sensitivity may develop around the coronary band and cause lameness.

Affected horses should be removed from the kleingrass source, fed good-quality hay, and protected from sunlight. Antibiotic or softening creams may be needed in severe cases of light sensitivity.

Alsike clover (Trifolium hybridum)

Ingestion of clover pasture, especially during wet seasons (dewy pastures); diet with high content of clover (especially blossoms) in pasture or hay.

Feeding on clover, especially blossoms at pasture or high percentage of clover in the hay. Usually seen in horses eating larger amount or grazing longer on clover than those with “dew poisoning.”

“Dew poisoning.” Light sensitivity—reddened skin after exposure to sun, followed by death of the skin or swelling and discharge. The muzzle, tongue, and feet are frequently affected.

“Big liver disease”: loss of condition, liver failure, neurologic disturbances, colic, diarrhea, death.

Care of skin lesions; removal of the horse from Alsike-containing pasture or hay.

Removal from Alsike-containing pasture.

Cocklebur (Xanthium species)

Uncommon; feeding on ground seeds or young seedlings; burs are toxic but rarely eaten.

Within hours of toxin ingestion, horses develop signs of depression, weakness, poor coordination, breathing difficulty, convulsions, and death. Signs are due to sudden liver failure. Horses that survive often develop longterm liver disease.

Treatment requires intensive supportive care. Mineral oil or activated charcoal may be given by mouth to delay absorption of the toxin.