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Question of the Week: My horse is eating tree bark

My horse has eaten the bark off the trees in his field. Should I be concerned?

17-May-11

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Ingesting parts of certain trees can cause health problems in a horseQ: I recently purchased a six-year-old gelding for trail riding. I've noticed that he drools when he is eating grain. I also noticed that he's eaten the bark off two oak trees in his pasture. My other horse has been turned out in the same field for years and never touched the trees. Could the tree bark be harmful to him? Is he eating it because he's lacking something in his diet? I feed him a senior feed mixed with beet pulp.

A: Drooling while eating grain is a common indicator of dental issues. Since you’ve recently purchased this horse, it’s likely you haven’t yet had a chance for your veterinarian to visit for a dental check up and you may not know the last time he’s had his teeth floated, if at all. Have your vet out for a dental visit soon. She will likely open your gelding’s mouth with a speculum, allowing her to take a good, detailed look at all his teeth, including the molars deep in the back of the mouth. Missing, broken, or otherwise unhealthy teeth frequently cause horses to drool while eating. Sharp edges on teeth created by uneven wear will create sores on the tongue and insides of the cheeks, resulting in excessive drool production. It may also be likely your horse injured the inside of his mouth by the bark that he’s munching on. Sometimes even bits can wear and cause oral injuries. All of these causes can be examined with a trusty mouth speculum, maybe some sedation, and of course a good flashlight!

Red clover in the pasture can also cause excessive drooling in horses (referred to as “slobbers”), but this type of drooling is usually seen constantly, not only when the horse is eating grain. The red clover that causes “slobbers” is infected with a fungus that produces an alkaloid toxin called slaframine. Other than causing a mess, this toxin is completely benign and the slobbers stops as soon as the horse is taken off the clover.

In terms of stripping bark off trees, your horse may be exhibiting what is called a stereotypic behavior, or vice, like cribbing. It is possible this is a bad habit your horse has brought with him to his new home, or a sign of boredom. You might consider supplying your gelding with some enrichment activities such as a HorseBall to play with in the pasture to occupy his time, his brain, and most importantly, his mouth.

Other than being destructive and annoying and eventually lethal for the trees, bark chewing isn’t typically “bad” for your horse. However, your horse may be more prone to choke, as a piece of hard bark may lodge in his esophagus. Intestinal impaction is also a risk.

Oak trees can be toxic to horses, although cattle seem to be more sensitive. Oak buds, leaves, and acorns contain chemicals called tannins which, when eaten and metabolized, can cause both renal and gastrointestinal damage. Fortunately, the bark of oak trees is non-toxic and horses generally don’t like the taste of acorns or oak leaves. Also, a few nibbles of the leaves or a mouthful of acorns is not enough to cause toxicity in your horse. Equine oak toxicosis is usually only seen in starvation cases where there is absolutely nothing else in the pasture for them to eat.

While eating bark can be considered a form of pica (a tendency to each substances other than normal food), unless this gelding came to you extremely malnourished, I wouldn’t think a mineral balance is to blame. However, your veterinarian may want to draw blood from your gelding and submit it for a mineral panel, just in case.

The senior feed you are giving him is very likely a complete, well-balanced ration that normally doesn’t require any supplementation. Make sure your gelding has access to plenty of roughage (in the form of pasture or hay), as sometimes horses will crave roughage when they aren’t getting enough. A good rule of thumb to remember is an average sized horse should consume about 1 to 2% of his body weight in roughage each day. Sometimes it’s difficult to visualize the true amount of roughage a horse needs on a daily basis – weighing hay flakes on a scale may help put the required amount in a better, more objective perspective.

Placing an equine salt/mineral block out in the field is another fairly easy tip to try. Some horses crave more salt in their diet than others and conversely, some horses do not touch a salt block at all. Of course, an old-fashioned fence around the trees may end up being the easiest method of all, that is, if all the trees are conveniently clustered together or if there are only a few!

--Anna O'Brien, DVM

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Question of the Week: My horse is eating tree bark

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Reader Comments

Shireen    Leeton, NT

8/15/2014 10:56:34 PM

We bought our property14 years ago, and planted hundreds of trees , from Australia we planted Eucalyptus which horse will not eat as they are pest resistance, able to withstand drought and cold, it's natural for horses to pick at trees, it's what they would do in the wild.

Janice    Waseca, MN

5/23/2011 5:06:37 PM

The soil in our area is lacking salinum. My horses will tear at the bark on trees, or the fences without the salinum enriched salt block. It can be a simple fix, and a good way to remember to always keep salt available for your horses.

jockey girl!    horseland, IL

5/22/2011 1:09:58 PM

hes most likely bored.poor horse:(

Galadriel    Lothlorien, ME

5/21/2011 11:17:27 PM

Interesting.

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