horse aggressive in the stall

Q.My 24-year-old mare has gotten rather grumpy as she’s aged. She does not like other horses in her personal space, especially geldings. This has started to become a problem, because she will pin her ears and even act like she’s going to lunge through the window at the geldings when we lead them by her stall. Verbal scolding has helped a bit, but I’m concerned that she might accidentally bite a person leading a horse, when she’s actually going after the horse. Do you have any suggestions on what’s making my horse aggressive in the stall and how I can stop it?

Andi, via e-mail

A.A horse who displays aggressively toward other horses walking past his or her stall can be found in nearly every barn, and your concern about incidental injury to a person is justified.

For example, a professional trainer and friend of mine was leading a horse down a barn aisle when another horse stretched his head out over his stall door and laid his ears back in a threatening manner. My friend waved his free hand up toward the horse, and in the blink of an eye his finger was gone!

Let’s break down what might make a horse aggressive in the stall and how we can squelch this behavior.

Why are horses aggressive toward others passing by the stall?

To modify this unwanted and potentially dangerous behavior, it helps to understand why a horse might be grumpy in this situation. One reason is because other horses passing in the barn aisle are physically close, and less distance generally equates to a greater threat. Another reason is that horses are usually fed hay and grain in their stall, and food is a valuable and defendable commodity.

Even more problematic is that once it begins, the aggressive behavior often persists because, from the horse’s perspective, it works every time! When the stalled horse lashes out with pinned ears and a sour face, the other horse always moves away as he continues down the barn aisle. An association between the aggressive display and “intruder” retreat has been forged in the horse’s brain. Thus, the aggression is unintentionally reinforced and likely to be repeated. Decades ago behavioral scientists confirmed that this type of superstitious aggressive behavior can be created through inadvertent negative reinforcement.

Offensive social aggression can be triggered when a horse asserts ownership over a valuable resource such as food, but the situation you describe is more consistent with a defensive “keep your distance” message. At 24 years old, age-related physical changes such as arthritis and muscular stiffness could reduce your horse’s comfort and mobility, which might explain her increasing grumpiness when other horses approach.

How can the aggressive behavior be changed?

A veterinarian can help identify and provide treatment for any physical and medical issues that might be contributing to the aggression. Your horse’s distress and the risk that someone might be injured can also be reduced by rearranging the environment, for example, by blocking your mare’s view of passing horses or by moving her to a more private stall with less traffic.

If you suspect the aggression is due to resource guarding, it can be reduced by providing 24/7 hay access, putting food in multiple areas (e.g., in several haynets or spread around the stall), and using a puzzle feeder for grain, such as a Nose-It! Slow feeder ball. By distributing food across space and time, there is no stockpile to defend and the horse is never in a fasting state. Thus, she’s less motivated to behave aggressively.

Changing a horse’s attitude and behavior requires training. You mentioned using verbal scolding to stop the aggression when it occurs. Scolding might appear to suppress the unwanted behavior, but a downside is that corrections don’t improve the horse’s underlying anxiety and attitude. Another concern about verbal reprimands is that the person can become a “discriminative stimulus,” which means that the horse’s aggressive behavior will be curbed when the person is present but persist when the person is absent.

An effective behavior change strategy is to reinforce a different and desired response. For example, when another horse is led past the stall, your horse could be trained to turn away and orient toward a stationary target. Aggression and targeting are incompatible behaviors, meaning they can’t occur at the same time.

Using positive reinforcement to train an alternative response can also improve your horse’s attitude because she’ll learn that something pleasant happens when other horses walk past her stall. Targeting is a popular training protocol, and step-by-step instructions for stationary targeting are available in a new video produced by Shawna Karrasch/On Target Training.