Dogs are some of the most social animals you can keep as pets. This natural inclination to be social is part of the reason why they have been domesticated by humans for so long. They are descendants from wolves and are very territorial, love to live in social groups and have a strong emotional bond with whomever they consider to be a part of their pack. These behaviors make them easily trainable and is also why they are frequently used for protection, policing, hunting, and assisting with search rescue.
The doberman in this video has taken after its owner's interests in taking care of horses. Considering the horses as part of its pack, it's easy to see why people call him the "Horse Whisperer."