All herding behavior is modified predatory behavior. Through selective breeding, humans have been able to minimize the dog's natural inclination to treat cattle and sheep as prey while simultaneously maintaining the dog's hunting skills, thereby creating an effective herding dog.
Dogs can work other animals in a variety of ways. Some breeds, such as the Australian Cattle Dog, typically nip at the heels of animals (for this reason they are called heelers) and the Cardigan Welsh Corgi and the Pembroke Welsh Corgi were historically used in a similar fashion in the cattle droves that moved cattle from Wales to the Smithfield Meat Market in London but are rarely used for herding today.
Other breeds, notably the Border Collie, get in front of the animals and use what is called strong eye to stare down the animals; they are known as headers. The headers or fetching dogs keep livestock in a group. They consistently go to the front or head of the animals to turn or stop the animal's movement. The heelers or driving dogs keep pushing the animals forward. Typically, they stay behind the herd. The Australian Kelpie and Australian Koolie use both these methods and also run along the backs of sheep so are said to head, heel, and back. Other types such as the Australian Shepherd, English Shepherd and Welsh Sheepdog are moderate to loose eyed, working more independently. The New Zealand Huntaway uses its loud, deep bark to muster mobs of sheep. German Shepherd Dogs and Briards are historically tending dogs, who act as a "living fence," guiding large flocks of sheep to graze while preventing them from eating valuable crops and wandering onto roads.
Herding instincts and trainability can be measured when introducing a dog to livestock or at noncompetitive herding tests. Individuals exhibiting basic herding instincts can be trained to compete in herding trials.
The competitive dog sport in which herding dogs move animals around a field, fences, gates, or enclosures as directed by their handlers is called a sheepdog trial, herding test or stockdog trial depending on the area. Such events are particularly associated with hill farming areas, where sheep range widely on largely unfenced land. These trials are popular in the United Kingdom, Ireland, South Africa, Chile, Canada, the USA, Australia, New Zealand and other farming nations, and have occasionally even become primetime television fare.
Sheep dog at work at NTIF 2017.