Each breed of a dog comes with genetic traits that sway the dog to certain things. The Sheltie is the herding and the "ball!!!!"; Beagles it is tracking, greyhounds it is chasing... Pits it is a aggressive defense (?).
Anyway, I know there are sweet pits that would never hurt a fly, and others that are dangerous. I worry about the instinctive traits that pops out and locks its jaws onto something,,,,
As Judge Wapner said during "Animal Court" (PARA PHRASED FROM Memory) In all my years of hearing these (dog) cases, its never a collie that bites the chIld, its always the same breeds'