What specific type of dog was introduced to ensure the Flat-Coat possessed high intelligence and willingness to cooperate?

Answer

Collie-type dogs

Collie-type dogs were intentionally introduced to the ancestral pool to provide the necessary intellectual tractability and willingness to work closely with a handler.

What specific type of dog was introduced to ensure the Flat-Coat possessed high intelligence and willingness to cooperate?
Dogbreedlineagecoatretriever