It's a tragic story - five loose dogs (with a history of getting loose, no less) began attacking two foals. Their mothers' intervened and eventually had to be euthanized from their injuries.
The horses were being cared for by Serenity Equine Resue and Rehabilitation and on their home page, you can read that all five dogs were pit bulls. In the original Seattle Times report, the dogs are labeled as pit bulls as well.
Except they were not. Two were pit bull mixes. Two were mixed breeds, mutts. One was a Chihuahua mix.All five were mixed breeds, none were purebred "anything".
It is awful that these horses died. The owner of the dogs has a history of letting his dogs run loose. They have gotten into fights with other dogs. They have scared people.
None of that has to do with their breed, of course. Any dog can be aggressive and almost all mid-size to large dogs can cause significant physical harm (small dogs can too).
All of it comes down to human behavior. We have an owner/guardian unwilling to comply with common courtesy and the law by leaving the hole in his fence. We have a clearly understaffed animal control, sheriff's department who are unwilling to offer any other assistance than "shoot the dogs if they're worrying your livestock". It's a nasty cycle that has now ended in the deaths of seven animals. All because of one hole.