Happens often this time of year; the shelter Im interning at is probable full of escaped animals after all the fireworks last night. Even big dogs like that get pretty freaked out over the noise etc.
And almost all dogs have the POTENTIAL (not saying all do or will....please don't kill me) to eat/attack farm animals. And domestic dogs are one of the only species that will attack them just for the heck of it, without even being hungry. I think it has something to do with the domestication process that the connection between "hunt" and "food" was lost in the domestic dog.
Glad to hear that there is a happy ending on both ends of this; It's refreshing to hear about people who are interested in all kinds of animals (chickens...really?? o_O) and that the owners of the dogs are at least trying to care for them instead of just leaving them in the backyard while theyre on Vacation.