Give a stream of consciousness and then the final answer. Spike was a lop-eared yellow Mastador (Mastiff / Labrador Retriever mix) and a dog actor best known for his performance as Old Yeller in the 1957 Disney film of the same name co-starring Tommy Kirk, Dorothy McGuire, Fess Parker, and Kevin Corcoran. Spike was rescued as a pup from a shelter in Van Nuys, California and became the pet and pupil of animal trainer Frank Weatherwax.

Answer this question: what kind of dog was in old yeller?
To answer the above question, the relevant sentence is: Spike was a lop-eared yellow Mastador (Mastiff / Labrador Retriever mix) and a dog actor best known for his performance as Old Yeller in the 1957 Disney film of the same name co-starring Tommy Kirk, Dorothy McGuire, Fess Parker, and Kevin Corcoran.
So, the final answer is a lop - eared yellow Mastador ( Mastiff / Labrador Retriever mix ).