There are also some breed specific issues you will need to research if you want a certain pastoral type: for example those related to the Blue Merle gene in Border Collies, or hip problems in German Shepherds. (thehappypuppysite.com)
Due to the high occurrence of health problems with the double merles in other breeds we do not have or produce any dogs in our program with the dominant merle gene. (oldenglishbulldogpuppies.com)
Responsible breeding practices usually include avoiding genetic instances such as the double merle gene since the pups often have these deficiencies. (corepaws.com)