Common Name
Hound's Tongue, beggar'™s lice, dog'™s tongue, sheep bur, dog bur, glovewort, and woolmat.
Botanic Name
Cynoglossum officinale L.
Plant Family
An increasingly abundant noxious weed that is adaptable to disturbed soils, roadside, meadows, at both high and low altitudes.
Animals Affected
Horses, cattle
Hounds-tongue, first year rosette of leaves
Toxic Principle
Pyrrolizidine alkaloids. All parts of the plant are toxic, even when it is dried. Toxic dose 15mg of dried plant per kilogram bodyweight over 2 weeks induces severe liver disease. Pyrrolizidine alkaloids interfere with cell division, affecting especially the liver. The PA are cumulative in effect and cause severe liver fibrosis and eventual irreversible liver failure after several months.
Biennial, forming a rosette the first year of based leaves up to 18 inches long, densely hairy and tongue shaped. In the second year a 2-4 foot erect flowering stem is produced. Flowers are reddish purple in color and are produced from the terminal leaf axils. The fruits are pyramidal, separating into 4 nutlets which are covered in hooks (like Velcro) enabling adhesion to animal hair and clothing.
Weight loss as a result of chronic liver disease
There is no effective treatment for animals with terminal liver disease due to pyrrolizidine alkaloids as the liver changes are irreversible. Keeping the animal out the sun will relieve the photosensitization but not affect the underlying liver disease.
Nervous System
Abnormal behavior - excessive yawning, walking in circles, and depression result from liver failure (hepatic encephalopathy).
Integumentary System
Secondary photosensitization develops as a result of severe liver disease. White skinned (non-pigmented) areas become red, swollen, and painful before the skin dies and sloughs-off as if it is severely burned.
Hepatic System
Yellow coloration to the mucous membranes (jaundice), weight loss, diarrhea, rectal prolapse, edema of the legs, red urine (hemoglobinuria) are signs of severe liver disease.
Elevated serum liver enzymes, decreased albumin, and a liver biopsy that shows megalocytosis, fibrosis and biliary hyperplasia are diagnostic of PA poisoning.
Special Notes
Hounds tongue is rarely eaten by livestock when it is green, but when dry and incorporated in hay, it is palatable and retains its toxicity. Hounds tongue is listed as an important noxious weed in many States because it is aggressively invasive. It can be controlled by digging out the plants, mowing to prevent flowering and seed production and by the use of herbicides. Herbicide control: Picloram at 0.25-0.5 lb., 2,4-D, or dicamba at 1.0 lb., or metsulfuron at 0.6 oz./acre applied in spring provides control of houndstongue. Spring treatments with picloram,dicamba, or metsulfuron are more effective than fall treatments (Sebastian and Beck 1995). Chlorsulfuron applied 0.5 lb/acre gave complete control when applied any time beginning with the rosette stage until the bolted plant had attained 10 inches in height (Butterfield et al. 1996). References: Pfister JA, Molyneux RJ, Baker DC. Pyrrolizidine alkaloid content of houndstongue (Cynoglossum officinale L.). J Range Manage 1992. 45: 254-256. Baker DC et al. Cynoglossum officinale toxicity in calves. J Comp Pathol 1991. 104:403-410. Knight AP, Kimberling CV, Stermitz FR, Roby MR. Cynoglossum officinale (hounds tongue)--a cause of pyrrolizidine alkaloid poisoning in horses. JAVMA 1984, 185: 647-650.
Hounds tongue flowers.
Hounds tongue seeds - 4 nutlets.
Hounds tongue flowers and fruits.
Hounds tongue flowers
Severe secondary photosensitization