Why do ethically minded breeders caution against pairing two Merle dogs together?

Answer

This combination can dramatically increase the risk of severe congenital health issues.

Breeding two Merle dogs together is strongly advised against by ethical breeders because this double-dose inheritance significantly elevates the risk of serious, inherent health problems in the resulting puppies.

Why do ethically minded breeders caution against pairing two Merle dogs together?
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