If you go down to the river, you may see a fisherman. Ask him — they are almost always hims — whether a hook in a fish’s mouth hurts the fish, and you’ll hear what I always hear: “No. Fish don’t have any feelings. They don’t feel pain. A hook doesn’t hurt them.” If you go down to the stable, you may see a rider. Ask her — they are almost always hers — whether a bit in a horse’s mouth hurts the horse, and you’ll hear what I hear: “No. Even a very severe bit, in the right hands, can transmit extremely subtle, nuanced signals that cause no pain to the horse.”
Logic tells me that this can’t be true.
I have argued that a herd of horses is much like a school of fish or flock of birds, leaderless and choosing a course of action via collective decision making. I have argued that “respect” as is normally meant by humans, does not exist in the horse, and that humans often use it as a euphemism for “fear”. I do not dispute the existence of “dominance” in a herd of horses, but I have questions about what it is and whether the concept is useful. Thirty years ago, researchers were far from a consensus on how to define and measure dominance, and little has changed since then. Anything gets harder to talk about when we can’t agree on what it is.
Agonistic behavior is a group of social behaviors that relate to fighting. Agonistic behavior may include warnings (threats and displays), efforts to break off an unpleasant encounter (retreats, placation), fighting, and conciliation. Aggression is a subset of agonistic behavior. The word labels hostile or violent behavior, and may include threats of such behavior, but excludes retreats, placation, and conciliation. Aggression is much more common in captive domestic horses than in feral horse bands.2
Aggressiveness is a temperament in which a horse shows hostile or violent behavior toward a human, horse, or other animal. Aggressive horses are more likely to show threat displays under the right circumstances. In contrast, an assertive horse is confident and forceful. An assertive horse might be the first through the gate at feeding time; an aggressive horse might be more likely to bite another horse while waiting at the gate. A horse may be both assertive and aggressive.