Hypochaeris radicata
Asteraceae
Catsear; Cat’s Ear; Common Catsear; Hairy Cat’s Ear; Rough Cat’s Ear; Flatweed; False Dandelion; Summer Dandelion; Frogbit; Gosmore; Hypochaeris radicata; Hypochoeris radicata
Unknown toxic principle; suspected cumulative neurotoxic compound or toxin complex associated with Australian stringhalt in horses. The plant is associated with, but not conclusively proven as the sole cause of, stringhalt-like neuromuscular disease in horses.
In horses, signs are primarily neurologic and gait-related and may include stringhalt, exaggerated flexion of one or both hind legs, sudden upward jerking of the hind limb, hopping or goose-stepping gait, difficulty backing, difficulty turning, hind-limb hyperflexion most obvious at the walk, dragging of hind feet in some cases, muscle atrophy in chronic cases, laryngeal involvement or roaring sounds in some affected horses, weakness, difficulty standing or walking, and severe debilitation in advanced cases. In dogs and cats, serious poisoning is not well documented; possible signs after ordinary plant ingestion would most likely be limited to mild gastrointestinal upset such as vomiting, diarrhea, reduced appetite, or transient stomach irritation from eating non-digestible plant matter.
Hypochaeris radicata, also spelled Hypochoeris radicata in some older references, is probably one of the most widely distributed weeds in the world. As a result, the plant goes by a variety of names depending upon the country and region in which it is located. Names include Flatweed, Rough Cat’s Ear, Hairy Cat’s Ear, Catsear, Common Cat’s Ear, Spotted Catsear, False Dandelion, Summer Dandelion, Frogbit, and Gosmore.
The most common name is some derivative of Cat’s Ear, in reference to the softly lobed, hairy leaves, which somewhat resemble the ears of a cat. In North America, the plant can be found throughout the United States and much of Canada, where it is considered a widely distributed invasive weed in many areas. It is especially common in lawns, roadsides, disturbed soils, waste areas, low-quality pastures, and thin or overgrazed pasture systems.
In appearance, to all but the trained eye, this plant resembles the common dandelion in overall appearance and color. Both plants produce yellow composite flowers and basal rosettes of leaves. The differences include stem length, branching, leaf hair, leaf shape, and serration. Catsear generally has hairy, lobed leaves and flowering stems that may branch, whereas true dandelions generally have hollow, unbranched flower stems and more sharply toothed leaves.
As is the case with many other plants, toxic effects may be species-dependent. Whether this is a result of size differences, differences in physiology, differences in grazing behavior, or the amount and duration of exposure is not completely known. There is no strong documentation showing serious toxic effects of Catsear ingestion in dogs or cats, and for humans the plant is often considered edible, with the leaves sometimes eaten raw in salads, steamed, or used in stir-fries.
The main area of concern is ingestion of Catsear by horses, where the plant is associated with a potentially debilitating neuromuscular condition known as stringhalt, more specifically Australian stringhalt when linked to pasture exposure. By definition, stringhalt is the sudden exaggerated flexion of one or both hind legs in the horse, most easily seen while the horse is walking, backing, or turning. What may sound mundane, akin to a twitch or a tick, can become severe enough to totally debilitate the animal, leaving it unable to walk or stand normally.
Current veterinary references describe Hypochaeris radicata as associated with stringhalt in horses, while also noting that the exact toxin and causal mechanism remain uncertain. MSD/Merck lists Flatweed, Cat’s Ear, and Gosmore as associated with, but not definitively proven as the cause of, a neurologic condition in horses characterized by hypermetria or hyperflexion of the pelvic limb, especially in dry years. Oregon State Extension likewise describes false dandelion or flatweed as associated with stringhalt disease in horses and emphasizes management of infested pastures.
The relationship between Catsear and stringhalt appears to be cumulative rather than the result of a single casual bite. Horses are believed to become affected after consuming moderate to small amounts over time, especially when the plant becomes a substantial part of the available forage. This is why the disease is most often seen in horses dependent upon pasture for nutrition, particularly where pasture quality is poor, grass is sparse, weeds are abundant, and animals graze the same infested areas repeatedly.
Dry years, poor pasture conditions, overgrazing, low forage availability, and weed-dominated paddocks appear to increase risk. When desirable forage is limited, horses may consume plants they would otherwise avoid or may ingest Catsear incidentally while grazing close to the ground. Because Catsear can be aggressive in lawns and lowland pastures, it may gradually become abundant enough that chronic exposure becomes a practical concern.
The clinical condition itself is not primarily a gastrointestinal poisoning. It is a neuromuscular gait disorder. Affected horses may show sudden, exaggerated flexion of the hind limbs, especially at the walk, while backing, when turning, or when excited. One or both hind legs may jerk upward sharply. Some horses show a hopping, goose-stepping, or snatching motion of the hind legs. In chronic or severe cases, muscle atrophy, difficulty walking, difficulty standing, or laryngeal involvement with abnormal roaring sounds may occur.
The prognosis varies widely. Some horses improve after being removed from the affected pasture and placed on better nutrition, but recovery can be slow. Natural recovery may take months to years. Some horses recover only partially. In more severe cases, the animal may be so debilitated that euthanasia becomes the only humane treatment option. Surgical treatment, including lateral digital extensor tenectomy, has been used in some cases, but success is variable and does not replace pasture control.
For dogs and cats, the risk should be kept in perspective. Outside of an allergic reaction or ordinary stomach upset from eating plant material, there is probably little chance that a dog or cat would suffer serious consequences from a one-time ingestion of a moderate amount of Catsear. That does not make it a desirable pet snack, but it does mean the page should not present Catsear as a major dog/cat poison in the same way as Castor Bean, true lilies, yew, oleander, or red maple for horses.
The practical prevention rule is different for different animals. For dogs and cats, preventing chewing is common sense. For horses, preventing long-term grazing exposure is the key. Catsear should be controlled in pastures, especially where it becomes abundant, where forage quality is poor, or where horses are showing early signs of hind-limb gait abnormality.
Immediate Response to Catsear Exposure
- Remove the Source: Prevent further ingestion by removing the animal from Catsear, Flatweed, False Dandelion, low-quality pasture, weed-heavy paddocks, hay contaminated with the plant, or areas where Hypochaeris radicata is abundant.
- Identify the Animal Exposed: Determine whether the exposed animal is a horse, donkey, mule, pony, dog, cat, or other animal. Horses and other equids are the primary concern for serious Catsear-associated disease.
- Watch for Equine Gait Signs: In horses, monitor for exaggerated hind-limb flexion, sudden upward jerking of the hind leg, hopping or goose-stepping gait, difficulty backing, difficulty turning, hind-limb dragging, weakness, or difficulty standing.
- Do Not Wait if Stringhalt Appears: Any horse showing stringhalt-like movement should be evaluated by a veterinarian and removed from the suspected pasture immediately.
- Dogs and Cats: If a dog or cat chews Catsear, remove plant material from the mouth, prevent further ingestion, and monitor for mild vomiting, diarrhea, reduced appetite, or stomach upset.
Dogs and Cats: Supportive Care
- Expected Risk: There is no strong documentation showing serious toxic effects in dogs and cats from ordinary Catsear ingestion. Most concerns would likely be limited to mild gastrointestinal upset from eating non-digestible plant matter.
- Hydration: If vomiting or diarrhea occurs, ensure the pet receives adequate fluids to reduce the risk of dehydration.
- Gastrointestinal Protection:
- Kapectolin: To alleviate gastrointestinal upset and diarrhea, Kapectolin may be given at a dose of 1 to 2 ml/kg four times daily to help coat and protect the stomach lining.
- Sucralfate: Sucralfate may be used for gastrointestinal irritation because it reacts with stomach acid to form a paste-like protective barrier between irritated tissue and stomach contents.
- Dogs greater than 60 lbs: 1g every 6 to 8 hours.
- Dogs less than 60 lbs: 0.5g every 6 to 8 hours.
- Cats: 0.25g every 8 to 12 hours.
- Veterinary Care: Consult a veterinarian if vomiting or diarrhea is persistent, if the animal becomes weak or dehydrated, if blood appears in vomit or stool, or if an allergic-type reaction develops.
- Expected Recovery: In dogs and cats, the prognosis is good, and the pet should make a full recovery within 1 to 24 hours when signs are limited to mild gastrointestinal upset.
Horses: Stringhalt Management
- Remove from Infested Pasture: The most important first step for horses is removal from the original paddock or pasture containing Catsear, low-quality forage, weeds, and sparse native grasses.
- Improve Diet: Provide clean, high-quality hay and balanced nutrition so the horse is no longer dependent on grazing weed-heavy pasture.
- Pasture Control: Control Catsear in pastures, especially in thin, dry, overgrazed, or low-quality areas where the plant may become abundant.
- Veterinary Evaluation: A veterinarian should evaluate the horse’s gait, neurologic status, severity of hyperflexion, and whether other causes of abnormal gait must be ruled out.
- Monitor Progress: Recovery, if it occurs, is often slow. Improvement may take months, and in some cases recovery may take years or remain incomplete.
Veterinary Treatment Options for Horses
- No Simple Antidote: There is no known specific antidote for the suspected Catsear-associated toxin. Treatment is focused on removing exposure, improving nutrition, managing gait dysfunction, and supporting recovery.
- Mild Cases: Removal from the infested pasture, dietary control, and improved forage are often the most important and most successful interventions in mildly affected animals.
- Surgical Treatment: Lateral digital extensor tenectomy has been used by veterinarians as a treatment for stringhalt, with variable results and a reported success rate of slightly over 50 percent in some discussions.
- Phenytoin: Phenytoin has been used in the management of Australian stringhalt. Improvement may be seen in gait abnormality at the trot and canter, although improvement at the walk or while turning may be less consistent.
- Severe Cases: In severe cases where the animal is unable to walk, stand, or maintain quality of life, prognosis may be poor and euthanasia may become the only humane option.
Pasture and Prevention
- Inspect Pastures: Regularly inspect pastures, dry lots, roadsides, and low-quality grazing areas for Catsear, Flatweed, and False Dandelion.
- Reduce Overgrazing: Avoid overgrazing because thin pasture allows Catsear and other weeds to become more dominant and increases the chance that horses will consume them.
- Provide Forage: Keep horses supplied with adequate hay or desirable forage so they are not forced to rely on weeds for nutrition.
- Manage Dry-Year Risk: Be especially cautious during dry years or periods of poor pasture growth, when Catsear may remain available while desirable forage declines.
- Remove or Control the Plant: Use appropriate pasture management, reseeding, mowing, hand removal, or professional weed-control guidance to reduce Catsear where horses graze.
Prognosis and Recovery
- Dogs and Cats: Prognosis is excellent when signs are limited to mild gastrointestinal upset after a one-time ingestion.
- Horses with Mild Stringhalt: Prognosis is better when signs are mild, the horse is removed from the affected pasture early, and nutrition is corrected before severe gait dysfunction develops.
- Horses with Severe Stringhalt: Prognosis is guarded to poor when the horse is severely debilitated, unable to walk normally, unable to stand comfortably, or suffering advanced neuromuscular dysfunction.
- Recovery Time: Recovery may range from a few months to a few years, and some horses may not fully recover.
- Prevention: Prevent further ingestion of the plant, remove horses from infested pasture, improve forage quality, and consult a veterinarian when stringhalt-like signs appear.