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Burdock a sticky eye issue for cattle and horses

Heather Smith Thomas Published on 24 February 2014
Horses by burdock

Some of the best inventions are inspired by nature. The idea for Velcro, a handy closure replacing zippers, buttons, tying, etc., came from observing tenacious seedheads of the burdock plant.

A Swiss engineer developed Velcro after examining the microscopic hooks on the ends of these spines.

This wonderful clinging ability is great for kids’ boot closures and other uses – but not so great when burrs stick to your clothes, gloves or animals’ hair.

Horses’ manes and tails become matted. Wads of burrs encase a cow’s tail and ears. A native of Eurasia, this hardy plant was brought to North America by burrs stuck in the hair of imported animals.

When ripe, the burrs contain hundreds of tiny hooked slivers. If a sliver gets into an eye, it can cause inflammation.

The cornea may become inflamed and ulcerated; the eye may turn cloudy and have a white spot or pink bulge.

In cattle, the problem may be mistaken for pinkeye, but pinkeye is a summer problem when face flies spread infection from animal to animal.

By contrast, burdock slivers may get into an eye in fall or winter – any time after burrs are ripe. A sliver may embed in the eyelid, where it scratches the eye every time the animal blinks, or under the third eyelid, creating an ulcer on the eyeball.

The sliver is so small that the tools used by a veterinarian to examine an eye (focal light and magnifying lens) may not be powerful enough to locate and identify the foreign object.

Ann Dwyer, DVM (Genesee Valley Equine Clinic, Scottsville, New York), says burdock is a frequent problem, especially in pastures that aren’t mowed. “We see eye problems starting about August, when burrs become ripe,” she says.

“I have a theory – my clinical impression – that what happens when the tiny sliver gets into an eye is more than just a mechanical irritation. There may be some chemical influence that makes it more irritating to the eye,” she says.

“Most cases in horses occur underneath the nictitans (third eyelid membrane). I have also seen it in other parts of the eye, such as the junction between the white part of the eye and the cornea, but at least 85 percent of cases are a sliver caught under the nictitans,” says Dwyer.

“The irritant (the sliver) is impossible to see, even with my biomicroscope, but could be in the cornea or caught in the mucosa of the nictitans, scratching across the eye.

By the time the owner brings us the horse, there may be a granuloma type of reaction (like the pink raised area on the eyeball in pinkeye),” she says.

In cattle the first thing you notice is the eye held shut, running tears. The sliver is usually caught under the lid and scratches the eye at every blink.

If the sliver remains embedded, the constant irritation and damage usually results in the cornea turning blue, often with a white spot or ulceration in the irritated area.

It looks a lot like pinkeye, but burdock irritation is common in fall/winter whereas pinkeye is a summer problem.

The affected animal has tell-tale burrs stuck to the hair coat. It’s almost impossible to find the microscopic sliver with an on-farm examination.

Cattlemen have treated these eyes with topical medication, injections of antibiotic/anti-inflammatory drugs into the inside membrane of the eyelid, and stitching the eye shut.

The infection resolves over time as the tiny sliver dissolves and the body gets rid of it, but heals quicker with medication.

Treatment

“I have good success treating these eyes just presuming the burdock sliver is caught in one of those areas. I sedate the horse heavily, prop its head up on bales of hay and use a topical and local anesthetic so the horse doesn’t feel anything.

Then I scrape both the inner aspect of the cornea where we see the lesion, and the inner aspect of the nictitans to remove the sliver,” says Dwyer.

“I use a hemostat – a surgical instrument with a little gripper. The gripping part has stripes, which give it just enough abrasiveness to provide the force needed without cutting.

I open it up, put the open jaw against my thumb and use it like a person would use a butter knife to scrape something.

“Often the inside layer of the mucosa of the nictitans has a local blood vessel pattern that looks like rivers and their tributaries.

I presume that where blood vessels are showing, this is pointing the way to where something is buried and causing the irritation. I scrape that area until it bleeds.

Blood is not a problem on the surface of the eye, so it doesn’t matter if there’s some bleeding from that membrane after I scrape it,” she says.

“I’ve found that almost any topical antibiotic is sufficient to deal with possible infection while the eye is healing. In about 90 percent of these cases, one treatment is enough and the condition resolves.

Sometimes I have to treat twice, and I presume that I just didn’t get the tiny sliver the first time.”

“In large pastures (such as rangeland), there may not be a practical way to control burdock, but in smaller pastures like we have here in the East, it can be eliminated by chopping or spraying.

It can be expensive to treat an animal for this eye problem because it takes sedation and local anesthetic (and a few weeks of follow-up treatment), so prevention is important. Fly masks might help keep horses’ eyes protected,” she says.

An untreated eye may eventually resolve because the body’s inflammatory reaction dissolves the tiny sliver.

Controlling burdock

Dr. Don Morishita with the University of Idaho’s weed science department, says the best way to control burdock is to attack when it’s most vulnerable.

Seedheads mature by mid-August in southern areas and later in northern climates. You can eliminate burr problems by chopping the plant before it’s mature enough to make seeds. Several broad-leaf herbicides will kill burdock if applied properly, says Morishita.

Cow that has been in the burdock

Burdock is a biennial; it lives for two growing seasons. The first year, it doesn’t grow tall or bloom; it grows leaves and accumulates food reserves in roots, like a carrot (also a biennial).

The second year, it grows a deep taproot and tall stalk, producing flowers that become burrs. This exhausts food reserves in the root, and the plant usually dies after burrs mature.

After the stalk comes up, it is harder to kill with herbicides. The plant is sending food up from the roots instead of down, according to Morishita.

Burdock is easiest to kill the first year, in the rosette stage (circular cluster of leaves, no tall stalk). “Apply spray when the plant is putting food into the root; you have to get herbicide into the root to kill the plant.

Use a broad-leaf herbicide like 2,4-D that can move down into the root. If you spray early in the spring, you kill new sprouts and last year’s rosettes (plants that are trying to create more food reserves in their root for their big push to complete second-year growth and make burrs).

“You have to spray early to get the second-year plant. After the stalk comes up, it is harder to kill. If you spray in the fall, you are killing this year’s rosettes – plants that would mature and create burrs next year.

“Fall is a good time to spray burdock (as long as it isn’t water-stressed) to kill young plants that are storing food reserves for next year’s growth.

By contrast, in spring the second-year plant is taking food from its roots to produce leaves, tall stalk and blooms. The food is going up, and it’s harder to get the herbicide down into the root.”

When using herbicides to kill burdock, don’t overdo it. “If you use too much, it quickly kills the leaves and doesn’t get down into the taproot. The root survives to regrow.

You want a slower kill so leaves survive long enough to transfer herbicide down into the root to kill the whole plant,” he explains.

Chopping or mowing is effective, but you must do it at the right time or the plant will regrow from the root. “The best time is after the stalk is budding but before burrs are ripe. At that point the food reserves are so low in the root that it cannot regrow,” says Morishita.

It may take several years to eradicate. “A large plant can produce 200,000 to 400,000 seeds that may survive two to 10 years. Even though you chop or spray the plants, there may be viable seed in the ground.”  end mark

Heather Smith Thomas is a freelance writer based in Idaho.

PHOTOS

TOP: Spraying burdock early will prevent it from growing too tall. Photo courtesy of Ann Dwyer.

BOTTOM: Since burdock is biennial, its conditions will take two years of control among livestock. Photo courtesy of Heather Thomas.

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