Incompatible Horses: Bickering Minis

Q. Within the past three weeks we have purchased our second Miniature Horse, a 10-year-old mare in foal. When the mare arrived at our farm, we assumed that she would be a good companion for our two-year-old Miniature mare. We also expected that there would be some adjustments for all of us. We have them pastured together with separate, but side-by-side run-in stalls. They are fed separately, each is given separate exercise with the other watching, and each is given an extreme amount of love and attention.

We thought that the two of them were adjusting.  We are aware that the dominant mare sometimes needs time to get established, but they still seem to be at war. Mostly it is the younger who continually gets bitten and kicked. Is this perhaps because the older is pregnant? What do you suggest at this point? Separate them? We don't want this trauma to harm the younger horse or put the pregnant one in such a turmoil that she is in jeopardy of losing the foal. Many people have advised us to let them work it out. Others recommend separation. Please respond with your recommendations.


A. The conflicting suggestions are not unusual and actually quite understandable. It's always difficult with these regrouping incompatibilities to know how long to ride out the bickering, when to try again if conditions change, or when to give up. I can give you yet a third reasonable suggestion to consider. Sometimes it works well to put the two battlers in side-by-side paddocks with plenty of space in each side.  This will enable one or both to stay away from the fence line. It will also allow them to make peace and buddy up along the line. Sometimes two animals that have been unfriendly seem to work things out through the fence without any injury. You'll get an idea from the time they spend near each other when it might be right to try to open the gate.  When you allow them together again, hopefully the peace will continue. Occasionally, one will start provoking the other's wrath again.

Often these incompatibilities change when another animal comes along.  While I'm not suggesting you go buy another horse, if a gelding or another young female were added, things might quiet down. If this were on a farm with other possible herdmates easily available, we might suggest playing around with other combinations or with a third horse in the same pasture.

You asked for my recommendation. First, let's address your questions about the pregnant mare. I wouldn't think it's likely that the pregnancy is a significant factor contributing to the aggression nor that the aggressive interactions would adversely affect the pregnancy, especially if they have plenty of space even if left together.

Before I could give you a recommendation on what to do right now, we would need to look closer at the situation and exactly what is going on. Under what specific circumstances is the aggression evoked? Where and when does it happen? What are they fighting over? Is it food-related? What are you feeding them? Maybe they don't have enough grazing appetite or opportunity to keep them occupied? Grain can exacerbate aggressive tendencies, and horses don't usually fight over grass. Does it look like the younger one is trying to play? Mature mares don't usually play, so maybe the younger one is pestering the older one to play. But that would rarely lead to contact battles. Do you have any social behavior history on the older mare? What about the younger mare? I assume they are both well-behaved around people.

While we're on the subject, isn't it rather amazing how most horses do get along fairly well with all the arbitrary groupings and regroupings they experience in life? This is not at all the way it is with horses in natural social herds or even with our modern domestic stock that are allowed to live in natural social groups for any major length of time. Horses tend to form very tight, long-lasting group bonds.  They naturally stay with their group and fight off or at least avoid any intruders. In contrast, in our ordinary domestic horses that are regrouped, there are some incompatibilities, particularly when we give them limited resources like feed and waterers to bicker over. But for the most part, we take our horses here, there, and everywhere and expect they will settle in before major damage is done. Maybe this greater social flexibility in our domestically managed horses is that they have opportunities as young horses to get used to all this reorganization.

About the Author

Sue McDonnell, PhD, Certified AAB

Sue M. McDonnell, PhD, is a certified applied animal behaviorist and the founding head of the equine behavior program at the University of Pennsylvania's School of Veterinary Medicine. She is also the author of numerous books and articles about horse behavior and management.

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