Definitely not your fault. For the most part, dogs and chickens just don't mix. Unless it's a specific breed of dog specifically trained just for the purpose of keeping chickens alive, most dogs have the instinct to kill.It's just in their nature.
I had that happen with a batch of guinea keets. My husband wanted to let them out to graze for the first time (he hates cages) and I was about to leave for the store. The dogs were in the house and his brother didn't know that Arthur was about to let the guineas out and he released the dogs into the yard. I had not yet introduced the dogs to the guineas and told them that they were mine and not wild life. In under one minute disaster ensued. My half Lab, 1/4 Border Collie, 1/4 Golden Retriever female saw the guineas and 1,2,3,4,5, took down five guineas before she could be stopped.
This time with my chickens I have brought them one by one into the house and introduced them to my dogs and told them that these are mine and petted them and then petted the chickens to show that they are not wild life. The dogs and the cats ignore the birds entirely. The only time one didn't is when one of them got loose in the front yard and my Sheltie/Lab cross tried to herd her back away from the street. That stopped her from getting away from me and I told Porche that she was a good girl.
Now I don't get after my dogs or cats for killing mice, rats, wild birds, squirrels, rabbits or chasing racoons and possoms off. Between the two they have established a kill zone that few dare challenge. The squirrels don't even try for my black walnuts. I occasionally see a bold rabbit hop briefly through the yard. So it is possible to get them to distinguish between those animals that are free game and those that belong. In truth the most amazing to me is the cats. They have all been raised from kittens to coexist with the dogs and they seem to follow the dogs lead on how to view the birds. I didn't have to do any additional explaining to the cats. The only dog I have to be careful of is my Beagle, Lucky, because she doesn't like the chickens (or the cats) to crowd her space and will snap at either but not pursue. The cats figure out pretty quick to give her a wide berth. I am sure the chickens will too.
