As there are many dogs between the weights of 55-80 lbs the Size 4 Comfort Trainer is the most commonly used size. It can fit a retriever, shepherd or Doberman, among other breeds. The back strap ensures a custom fit and the rounded nose band will not move into the dog's eyes or injure the muzzle. The open mouth design means that the dog will quickly acclimate to wearing it and learn at a more accelerated rate.