Additional information from mare’s owner:

I wrote to you about the 7 yr old that runs circles in her paddock. She is kept in the paddock about a 1/2 acre. She is not ridden daily. Her diet is grass hay. She is an only horse at this time. We are getting another horse in a week or so. However, the last time she was put in with another horse she ended up kicking him pretty badly, so I do have concerns about that. She is a dominant mare, however she has done well with other horses in the past. Thanks for your help.

Link to previous post: Running Laps in her Paddock!

Response:  

One half of an acre is not much pasture for an adult horse, and since your mare is not ridden frequently, your mare is most likely exhibiting high energy levels due to inadequate exercise. Although one half of an acre is adequate in terms of animal welfare, I normally try to keep my horses on a minimum of 1 acre per horse. By increasing her activity level (slowly if she’s not currently in shape or used to much exercise), the behavior will most likely be reduced. However, she may also be performing for another reason.

Additional causes could include: trying to evade flies or other bothersome insects, excitement that it’s feeding time, excitement when she sees other people or animals (regardless of species), or performance of a stereotypie (such as fence pacing). Stereotypical behaviors are often caused by one or more of the following factors, boredom, lack of exercise, excess feed, genetics (high strung temperament), frustration, social deprivation, or stress. When a horse performs a stereotypical behavior, the horse repeatedly performs a rather ritualized behavior without an apparent purpose for its actions. Horses appear to perform these behaviors as a way to keep themselves occupied or “busy”. Ambulatory stereotypies include fence pacing, running in circles, and stall pacing, to name a few. Lack of roughage in the diet and boredom can incite or increase stereotypical behavior. Since your horse does receive an all roughage diet (grass hay), boredom or social deprivation are the likely causes if your horse is performing a stereotypical behavior.

Treatment of stereotypies usually involves removing the underlying cause. For example, if your horse is lonely and performing the stereotypie due to social deprivation, providing a companion, such as a goat, chicken, pony, or another horse should alleviate the problem. Increasing the frequency and/or duration of exercise will often reduce stereotypical behavior if it is performed due to boredom or excess energy. For more on stereotypical behavior, see my post on the Difference Between Stereotypies and Vices.

You noted that your horse is a dominant mare, so it will be especially important to make sure your new horse is properly introduced to your mare before they are turned out together.