Instructions
Look at the body size. The merle Shetland sheepdogs are small and compact, usually around 13 to 16 inches tall. The old English sheepdog is usually between 20 and 24 inches tall, making it several inches taller than a merle. The collie is usually around 22 to 26 inches tall.
Consider the appearance of the dogs. The Old English sheepdog is square, compact and tough looking with high sloping shoulders and a lower back-side. It has fur covering its eyes and is generally black and white in color. It has a short "bobbed" tail in general. The merle and collie look similar, but the merle Sheltie is a miniature and has a more blunted head when viewed from the front. Both dogs have a long tail and a similar shape to the face, which is less square than the Old English sheepdog.
Look at the dog's temperament. The temperament of the merle Sheltie differs from the temperament of both collies and Old English sheepdogs. A merle Sheltie is a natural herder and will try herding the family. Merle Shelties are also suspicious of strangers and might bark or even bite. They are good family pets if socialized with the family from puppyhood. Collies are even tempered, loyal, friendly in nature though protective of their family. They are less prone to biting or suspicion of strangers unless the stranger gives them a feeling of discomfort in any way. The Old English sheepdog is completely different in temperament and is prone to puppy-like and clownish behavior. They might try herding, but will do so by bumping into people -- not nipping. All three types of sheepdogs are good with children and families.
How to Tell the Difference Between Merle Shetland Sheepdogs & Regular Sheepdogs
Sheepdogs are the dog breeds that were bred for herding animals. The term "merle" when referring to a Shetland sheepdog, or Sheltie, is related to the coat colors and style. When looking at the differences between the merle Shetland sheepdogs and other Shelties, several differences arise.