Mysterious Eye Inflammation Traced to Plant Burrs

Fall and winter sometimes bring unexplained eye problems in horses and cattle, with irritation and inflammation, or corneal ulcers. Veterinarians at the Virginia-Maryland Regional College of Veterinary Medicine, Cornell University, and New York State College of Veterinary Medicine have recently discovered the cause. Some of the horses examined at these college clinics over the past several years had microscopic barbed "slivers" embedded in the eye--bristles from the seed heads of the burdock plant. A burdock sliver of this type is called a pappus.

According to William C. Rebhun, DVM, Department of Clinical Sciences, Cornell University, foreign bodies in the conjunctiva (the delicate membrane that lines the eyelids and covers the sclera--the "white" of the eye) of domestic animals are usually of plant origin. He noted that hunting dogs often get seeds, awns, and other plant parts in their eyes; cattle are constantly exposed to plant material in feed, bedding, and tall pastures; and although horses might get dirt and dust in their eyes during speed performance, most foreign bodies that invade a horse's eyes also are plant material.

Large seeds and pieces of hay or straw in the eye usually work their way to the corner, where tears wash them out. Occasionally, they are trapped under the eyelid and cause irritation and scraping of the cornea (the tough transparent covering of the eye), leading to keratitis (inflammation of the cornea) or erosion or ulceration of the cornea. But large foreign particles usually can be seen during an eye examination and flushed free or removed.

By contrast, tiny foreign bodies less than 3 millimeters in length can be hard to locate and remove. Tiny slivers can easily become entangled in the folds of the eyelid lining. When caught under the lid, embedded in the lining, they create a sore by scraping against the eyeball each time the animal blinks. As Rebhun explains, their presence under the eyelid usually affects the area of the cornea opposite the affected lid, creating corneal abrasions, erosions, or ulcers. Symptoms include sensitivity to light and holding the affected eye closed, discharge and weeping of the eye, contraction of the pupil, and positive fluorescein dye uptake at the site of the corneal damage--all of which might mislead the examining veterinarian into making a diagnosis of corneal injury. Rebhun pointed out that an embedded foreign body might not be suspected until the corneal damage fails to respond to conventional therapy (topical antibiotics and drugs to keep the eye dilated) within a reasonable period.

He said that the plant material responsible for small conjunctival foreign bodies in horses can originate from a wide variety of plant types, but in the northeastern United States, burdock pappus bristles are the most common source. They are also a problem in the Northwest, as many ranchers have discovered with recurring fall and winter eye problems in horses and cattle.

Burdock (Arctium minus) is one of several plants that produce seeds that stick to the fur or hair of animals, or the clothing of humans, as a way to spread to new sites. Cockleburr (more low-growing than burdock, with smaller, egg-shaped burrs) and burdock (which has large composite leaves and grows six feet tall or more, with round prickly burrs) stick to anything that brushes by, due to the hooks and barbs on the seed heads. It was this tenacious design that inspired the inventor of Velcro.

The tall burdock plant (a native of Eurasia, probably brought to this continent by seed burrs stuck to imported animals) puts forth clusters of round burrs that easily become caught in horses' manes, tails, and fetlock hair if they happen to be grazing where the plant is growing, or if they are ridden through burdock-infested thickets. Burdock thrives in moist soils and is often seen along fencerows, roads, and waste areas. It often grows in shady wet places like creek bottoms, growing in among the brush or along ditchbanks. Cattle that go into the brush for shade or to graze the undergrowth often become covered with burrs that adhere to the hair and become matted. The burrs can be difficult to groom out of a horse's mane or tail.

Burdock flowers in late summer, producing a composite seedhead in the form of a burr that matures by mid-August in southern areas, later in northern climates. When the seeds are ripe, they release hundreds of microscopic barbed slivers. When the burr is shredded during attempts at removal, the seeds are scattered and the microscopic barbed pappi are released. Even if you pull off burrs that stick to your clothes, some of the slivers might remain, causing itching when the clothing is worn again. Slivers can become embedded in human flesh, causing irritation. The sliver is too small to see with the naked eye and therefore difficult to remove.

Burdock pappus bristles are much smaller than expected, when looking at a complete burdock burr. Few people are aware of the danger to horses and cattle (as well as dogs, cats, and humans) posed by microscopic barbed slivers enclosed in each burr with the seeds. The tiny bristles are found at the bases of the florets (the small individual "flowers" within the burr) and later remain in clusters on top of each tiny seed within the burr when it dries out.

If one of these slivers gets into the eye, it can cause inflammation and infection, creating a problem that might puzzle a veterinarian, since the microscopic sliver can elude traditional detection efforts. The pappus usually becomes caught in an eyelid or third eyelid, where it then scratches the surface of the eyeball with every movement of the eye or lid, creating irritation and pain. The inflammation persists and does not respond well to treatment. The cornea can become inflamed and ulcerated; the eye might turn cloudy and have a white spot or bulge on it.

In cattle, the problem might be mistaken for pinkeye, but is mystifying to owners and veterinarians because pinkeye is a summer problem when face flies spread the infection from animal to animal. By contrast, the burdock slivers are most apt to get into the eye in fall or winter after the seed heads are ripe. This "winter pinkeye" was in the past puzzling, since there were no flies at that season and pinkeye should not occur.

The pappus sliver from the burdock seed is so small that the usual tools used by a veterinarian to examine an eye (a focal light and magnifying lens) might not be powerful enough to locate the foreign object in the eye, especially during an on-farm examination. Rebhun at Cornell said that location of the general area is crucial to pinpointing the exact location of the pappus, since the actual viewing of it can be extremely difficult without extensive magnification. Also, the inflamed and reddened conjunctiva can easily hide the sliver.

The veterinarian must narrow the search by looking at the portion of the eyelid that neighbors or abuts the damaged cornea during normal eye movements and blinking.

After discovering burdock slivers as the source of several eye infections in horses brought to their clinic in Virginia, researchers at the Virginia-Maryland College of Veterinary Medicine found that staining the eye with fluorescein dye made it easier to locate an embedded sliver. Then they were able to use a powerful magnifying lens to pinpoint the sliver and remove it with forceps. Once the foreign object--the cause of the continuing irritation--is removed, the inflammation and infection can be cleared up.

Cases In Point

Ten cases of eye inflammation due to frictional irritation from burdock pappi caught in an eyelid or third eyelid membrane were documented at the teaching hospital in Blacksburg, Va., during a two-year period (July 1989 through July 1991). All of these cases occurred in late fall through winter (late September to early February), and all were in horses which were pastured or exposed to pasture before the onset of their eye problem. Each of these horses had burdock burrs in manes, tails, or leg hair or had been pastured where there were burdock plants. All ten had been examined at least once (some as many as four times) by a veterinarian before being brought to the clinic; some had been suffering from eye irritation for up to three months before the foreign body was discovered.

In all cases, a 2-3 millimeter long (and less than 0.25 millimeter thick) foreign body was found in the upper eyelid membrane (six cases) or in the third eyelid (four cases), which corresponded to the locations of the corneal ulceration. In long-standing cases, a small raised area of local inflammation outlined the foreign body. The slivers, after being removed, were identified as burdock pappi. In six cases the slivers were removed by grasping with forceps, but the other four could not be grasped and were removed by vigorously scraping the surface of the inflamed conjunctiva with a scalpal blade.

After removing the pappus, all eyes returned to normal with minimal supportive treatment (topical antibiotics, with or without atropine), although the eyes that had been inflamed for longer periods (with more corneal granular tissue formation and scarring) took longer to heal.

The veterinarians said that in a number of other fall and early winter cases when no foreign body could actually be identified (but with conjunctival inflammation and an adjacent corneal ulceration), scraping the inflamed conjuctiva and following up with supportive treatment resolved the problem, removing the offending tiny sliver.

As suggested by Martin Furr, DVM, Dipl. ACVIM, one of the veterinarians at the Virginia clinic, if an animal has an inflamed eye that is not responding to treatment (topical antibiotics--sprays, powders, ointments--put into the eye, and atropine), a burr fragment should be suspected.

"Most injured or inflamed eyes will respond to standard treatments and show signs of improvement after three or four days of medication," he said. If an eye does not improve, Furr recommended taking the animal to a clinic with specialized equipment for eye examinations, where a burr sliver could be more easily detected and removed. He said that the characteristic corneal ulceration or spot of inflammation near the eyelid or third eyelid margins should make the examining veterinarian suspicious that a small foreign body (such as burdock) could be the cause.

A few years earlier, 10 horses with persistant corneal ulcers were referred to the large animal clinic at Cornell (Ithaca, N.Y.) and were eventually diagnosed with burdock slivers. Three of those veterinarians wrote a paper describing this condition ("Persistant Corneal Ulcers In Horses Caused by Embedded Burdock Pappus Bristles," by William C. Rebhun, Marion Georgi, and Jay R. Georgi).

All 10 horses had a history of inflammation in one eye (with sensitivity to light, eye closed, tears and discharge, and a positive fluorescein dye uptake on the injured area of the cornea for one to eight weeks before being brought to the clinic). The corneal abrasions, erosions, or ulcers had persisted
in spite of treatment with antibiotics,
antibiotic-corticosteroid combinations, and atropine. Some of the eyes had temporarily improved after treatment, only to relapse.

Complete examination of the eyes ruled out lid abnormalities, corneal foreign bodies, and other common eye problems; bacterial and fungal cultures from corneal scrapings ruled out infection as the cause of the persistant ulcerations. However, careful focal light examination followed by biomicroscopy (microscopic examination of living tissue) of the conjunctiva showed the tiny foreign body next to a corneal lesion or on the inside of the eyelid adjacent to it. A single burdock pappus was found in most horses, but one animal had 13 slivers removed, and another horse had three.

In order to locate and remove the tiny slivers, the horses were sedated and given a nerve block, along with a topical anesthetic. To make sure the foreign body was completely removed, the affected area of conjunctiva was grasped with mosquito forceps and a small portion of the membrane snipped off along with the embedded pappus. Follow-up treatment included topical antibiotic ointments three to six times a day, ophthalmic atropine ointment one to three times a day, and one to two grams of phenylbutazone (to reduce pain) orally twice a day. Once the offending burdock sliver was removed, the eyes healed within three to 14 days in all ten horses.

Like Furr at Virginia-Maryland, Rebhun said that persistant, non-healing epithelial (outer surface tissue) erosions or corneal ulcerations should lead the examining vet to suspect a conjunctival or corneal foreign body, such as a burdock pappus--if other possibilities have been ruled out. A thorough search of the conjunctiva in the eyelid overlying the damaged cornea could reveal an embedded pappus.

Backyard horses, horses at pasture where burdock might grow in wet or shaded areas, and draft horses with lots of hair at their fetlocks are often at risk for burdock slivers in the eyes. Several of the horses examined by Rebhun and his associates had obvious evidence of exposure to burdock, with burrs matted in the mane, forelock, tail, or fetlock hair. This type of evidence when a horse has a persistant eye problem should arouse suspicion of burdock bristles as the cause, although several of the affected horses at the Cornell clinic were well-groomed with no burrs.

Fall and winter are the most common times for burdock-caused eye problems, particularly in the northern parts of the United States since that is when the seeds are ripe and hanging on the plant, ready to latch onto any passer-by. The burrs can hang on the dead, dry plant all winter and into the spring. Sometimes the old dry plants will still be standing in the spring and animals can come in contact with the burrs at pasture even before the new plants have put forth any flowers or seeds. A horse might get a burr sliver in an eye at other times of the year if his bedding contains some shredded burrs, i.e., when burdock plants get baled with straw. For instance, several cases of burdock keratitis occurred in April and May in horses referred to the University of Wisconsin (Madison) clinic--horses which had been exposed to burrs in their bedding material or turned out into spring pastures after a winter of stabling (when burrs were still hanging on last year's dry plants).

Whenever you find burrs stuck to your horse's coat, mane, or tail, you can prevent the shattering and scattering of harmful slivers if you coat the burrs with baby oil or petroleum jelly before removing them. This will keep the tiny slivers from blowing about in the wind, where they might end up in an eye.

Burdock can be eradicated from a pasture by chopping it down before it is mature enough to bloom and put forth seeds. It also can be controlled with herbicides. This pesky plant spreads rapidly by scattering seeds on any passing animal, so if you know of any plants in your pasture, it is wise to get rid of them.  

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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