Since Blue Merle is not a colour found in the Pembroke Welsh Corgi breed (see information on Colours of the Pembroke Welsh Corgi) these dogs are produced by crossing Pembroke Welsh Corgis with other breeds that do have the Blue Merle patten.
Here are some of the common crosses used:
Cardigan Welsh Corgi
Because the Cardigan is also a “Corgi” it is the most common cross used as it has the most similarity to the Pembroke. However, the result is still a mixed breed dog, that is worth no more than any other Crossbred.
While this cross will produce larger dogs, Blue Merle Aussies are used also.
Rough & Smooth Collies
Another Blue merle breed, the Collies have very little similarity to the Pembroke but are able to produce the colour desired.
Similar to the Collies – the Shetland Sheepdog is closer in size to the Cardigan – and although they may develop a long coat they will just be referred to as “fluffy” Blue Merle Pembrokes