Why do some horses not like having their buddies taken out of their pen when they have to stay in?

The ancestors of our domestic horses were open plains grazing animals, for whom the strategy for survival from predation is "safety in numbers," and "never be caught alone." Just as our horses have inherited their beautiful bodies and ability to take off at speed that supported survival on the plains, so have they inherited their social behavioral tendencies for survival. Some of these inherited social behaviors of survival from the past we admire and take advantage of in sport, and some become problematic in how we keep domestic horses.

So this great survival tendency to "never be alone" is known in domestic horses as a problem–"herd bound" or "separation anxiety." It is an interesting and important question for behavioral scientists, and especially for those studying behavioral genetics and developmental behavior, why some horses adjust well to domestic management and others don't.

There is a lot of good material available these days–videos, books, magazine articles–on the natural social behavior of horses. The domestic horse has retained most of its natural behavior, and so understanding how horses "tick" in a natural herd condition can help you understand and often to help horses do better under domestic management