The curse of cat’s ear: Why you should keep it out of horse pastures

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Freshly removed cat's ear.
Freshly removed cat’s ear.

Pulling and spraying are the best remedies for an infestation of the dangerous weed cat’s ear — also known as flatweed, gosmore, hawkweed and false dandelion.

Cat’s ear — Hypochaeris radicata — looks like a dandelion on steroids, and horses will eat it, hungry or not. The bad news is that it has been associated with a neurologic condition known as “Australian stringhalt” or Pasture Associated Stringhalt (PAS), as opposed to traditional stringhalt.

Australian stringhalt causes abnormal gait, knuckling of the lower limb joints, and a “roaring” like sound caused by paralysis of the larynx. Both hind limbs and forelimbs can be affected. Some horses show only mild flexion of the hock at the walk, while others more severely affected will jerk their foot toward the abdomen, sometimes hitting it. The earliest reported case was before 1900 in South Australia.

The good news is that, if foraging is your thing, you can apparently eat it yourself, as the flowers are high in lutein and carotenoids, and the leaf extract has high levels of antioxidants. The top four inches of the stalks are apparently the most tender and tastiest. The bitterness of the leaves and roots is removed by cooking, and can be added into a salad, steamed or boiled. It is reportedly best eaten before the flowers appear.

Hypochaeris radicata or cat's ear.
Hypochaeris radicata or cat’s ear. Image by WikimediaImages

In 1953, New Zealand researchers analysed the chemical components of H. radicata and found it comprised 10-15% protein, 10-20% fibre, 1-2% calcium, 0.15-0.5% phosphorus, and 5-10 ppm of copper on a dry matter basis.

The plant, from the Asteraceae family, was originally native to Morocco but is now also considered native throughout Europe. The herbaceous perennial has been successful in its world domination, being present on all continents except Antarctica. It is an invasive weed in many countries and is classed as a noxious weed in the US state of Washington.

It is often confused for dandelion (Taraxacum officinale), as both plants carry similar flowers which form windborne seeds (dandelion has also been linked to outbreaks of stringhalt in horses, as have sweet peas and mallow). Another weed, hawkbit, also looks similar.  But cat’s ear grows taller, to about 80cm, and has a central taproot. Its name refers to the shape and fine hair on the leaves resembling that of the ear of a cat. There is also “smooth cat’s ear”, which has hairless leaves.

Cat's ear is usually fairly easy to pull out, and has a strong taproot.
Cat’s ear is usually fairly easy to pull out and has a strong taproot.

Australian veterinarian John Kohnke says the type of nerve damage associated with Australian stringhalt suggests a soil-borne fungus or mycotoxin that grows on the plant. When ingested, these toxins specifically affect the long myelinated nerves in the hind limbs and also the long left recurrent laryngeal nerve in the neck. Tall horses (over 17hh), thoroughbreds, older horses and draft breeds are said to be particularly at risk, and anxiety and cold weather are reported to increase the severity of clinical signs.

Evidence suggests that most cases of Australian stringhalt have occurred during or after hot weather with little rainfall. This has led researchers to another theory, that when stressed by environmental factors such as high temperatures or drought, cat’s ear produces one or more compounds that are toxic to horses.

Horses can recover from stringhalt, but the condition can be permanent. In Plants Poisonous to Horses An Australian Field Guide, Melissa Offord says the recovery time can vary from a few days to up to 18 months, with the average being six to 12 months.

Like many plants, cat's ear tends to close up on dull days.
Like many plants, cat’s ear tends to close up on dull days.

According to veterinarian Jane Boswell of the Liphook Equine Hospital in Hampshire in the UK, many cases of stringhalt recover spontaneously when they are moved to another paddock.

But in chronic cases, removal of the lateral extensor tendon just below the hock has given best results, though not all cases respond.

Unlike buttercup, Hypochaeris radicata is harmful when baled into hay. In their study Neurologic causes of gait abnormalities in the athletic horse, published in Equine Sports Medicine and Surgery, Elizabeth Carr and Oma Maher said there have been reports of horses developing signs of stringhalt after ingesting the plant in hay.

 

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