These predatory and prey instincts, that historically helped our much-loved pets to survive, can sometimes take over, which unfortunately can lead to distressing and dangerous situations for both animals and handlers.
Understanding why dogs chase
While our pet dogs are not direct descendants of the modern-day wolf, both the dog and the modern wolf descended from a common ancestor. It's from this wild ancestor that dogs have inherited a chain of seven predatory behaviours, including the behaviour to chase:
Orient – Eye – Stalk – Chase – Bite kill – Bite dissect – Eat
Some of these behaviours have also been honed (hypertrophied) by humans through selective breeding. Over time this has allowed different breeds to perform certain roles better and meet specific human needs.
Most dogs today are not kept as working dogs but as pets. However, being aware of your dog's natural instincts and the role that the breed was originally bred for will help you understand and train them.
While today's domesticated dogs may not chase with aggression or biting in mind, a horse doesn't know this and their reaction will be the same.
Why horses run
Horses have evolved to have natural flight and defensive behaviours because, historically, they were prey that needed to survive being hunted by other animals.
If the horse can't escape a threat, they'll attempt to defend themselves with their hooves. A dog could be seriously injured or killed if one of these flying hooves catches them.
For horses, the instinct to flee or defend themselves from any threat is ingrained and difficult for a rider to influence. However, with time and patience, you can train your horse to accept dogs.