Let me answer your last question first. It’s very unlikely that your filly’s ear-pinning, biting, kicking, and butt-turning behavior you’ve described is the result of that early experience in the pasture with the other mare’s attention. This cluster of “defensive aggression” responses is a fairly common normal variation in the behavior of foals dealing with human handlers. Her behavior is likely due to her basic temperament. We say this because the pattern tends to run in families, and it seems to be independent of early experience.

For example, over the years I have known several sets of full siblings that had this tendency for the quick butt turn and kick, and quick bite. People sometimes describe these foals as “over-reacting” aggressively to the situation. In my experience, this cluster of defensive aggressive behaviors seems to be associated with a related behavioral trait that we affectionately call a “large personal space requirement.” There are horses that seem to react sooner and more aggressively than most horses to the approach of a threat, whether it’s an animal, person, or whatever. They can get better with handling or get used to things, but when threatened, they are very quick to be aggressive.

To safely interact with such foals and to reduce their fear of people, we recommend going slowly and using an all-positive rather than a punishment approach. In general, you need to get the foal to realize that you are not going to hurt it, and that attempts at biting and kicking are not effective at stopping your interaction.

First, work on getting the foal to come head-first for a food treat. For young, nursing foals, food enticements and rewards are often not all that interesting or rewarding, and you may have to look for another primary reinforcer. If you find the foal likes to be scratched at the neck, you can get her to approach for that. If you can’t find something like that, a small dose syringe or squeeze bottle filled with corn syrup can be used to treat the foal. Just hold it out until the foal investigates and finds the sweet taste a few times on its own. It usually isn’t more than a few minutes before they become very interested in whatever it takes for a little sip of syrup. The only downside is that their lips and you get very sticky.

Once the foal is reliably approaching head-first, we introduce the halter, again with reward, then teach it to lead and tie. As with approaching head-first, we try to entice the foal with treats to do what we need and keep punishment or rough handling, pushing, and pulling to a minimum. The foal needs to learn positive behavior and not reach a fear threshold that sets off defensive aggression. Then we start on touching the body all over, again reinforcing the animal for tolerating manipulation, and going gradually at first to avoid provoking a kick or butt turn. If she should gesture toward the kicking or butt turning, try to safely ignore it and move right on to something positive. If the kicking has no effect on your behavior, it should stop. For the biting, again you need to send the message that it is not effective. A simple way to send that message and to be safe, especially when working alone, is to use a muzzle. You can buy a mini-size grazing muzzle that clips onto the halter (the soft rubber basket type that won’t hurt as much if you get whacked with it) or make a simple muzzle from an old plastic half-gallon water jug attached to the halter. Cut a hole in the bottom a few inches in diameter, so that the foal can’t bite you, but you can still give it the reward. Cut some holes for tying the makeshift muzzle to the halter with twine. This way the foal will toss its head to bite, but won’t be effective, and you can safely ignore the gesture. Once the gesture to bite stops, you can try without the muzzle.

If the foal is whirling its butt around too quickly, you can make a little barrier wall with straw or hay bales over which you can work for the first couple of sessions until the foal gets used to you touching it. Again, you can safely ignore the gesture of butt turning and continue the task. It is very tempting to try to discourage the biting with a whack to the lips, and if the timing is just right, it can be effective. But this punishment will set them back in a big way, even when well-timed and judicious. So our general approach, particularly for a novice handler, is to simply not even try hitting or verbally disciplining until well into the training when the foal has learned that we are not likely to hurt it. There are trainers who would argue this point.

When doing behavior modification exercises with foals, we find that wearing protective gear further facilitates ignoring the foal’s attempts to bite or kick. In addition to the usual helmet and safety vest, our gear for feisty foals like yours includes safety shoes with high leather tops, sometimes field hockey shin guards to protect against those sharp little hooves, and a heavy long-sleeved jacket to protect against bites. Some of us wear leather gloves and heavy jeans or chaps to protect from nips and kicks.

We also plan the work area to avoid wrecks. While you might say that the foal that crashes into the wall, kicks the pole, or flips over backwards “did it to himself,” in the bigger picture we’re responsible for all of the foal’s interaction with humans.

To make the most progress, we want to avoid any inadvertent crashes that reinforce the foal’s fear and defensive aggressive behavior with people. We usually work on a good non-slip surface and pad the work area with bales of straw or hay. An alternative work area is an outdoor paddock with good sod footing.