I don't know of anything the pups can catch from sheep. The pups are still young. I would wait until they are atleast 8-9 weeks old before putting them out with those giant sheep. The sheep may spook and trample them at this age. I don't see anything wrong with it really. I don't know much about herding breeds or evaluations. I'm a working group girl. If anything it's a little socialization for the pups.