We have 2 Pyrenees field dogs and both killed chickens and guineas when we got them as adults.
First one, I merely held the chicken up and yelled at him. Required 2 chickens and 1 guinea.
Second one (younger) required more before getting hit across the face with last chicken.
Pyrenees can be trained. It’s a shame these kids did not invest the time and effort needed.
Some dogs are virtually untrainable against their natural hunt & kill instincts.