Sorry for your loss. When I first got chickens, some jumped over the 4 foot fence into my yard as young pullets. My golden retriever chased one 3 different times over a period of a month. The only one that died had no scratches or wounds. If they get internal injuries they usually will not live. While I trained my dog to never come near the chickens again, it's hard to do when a neighbor's dog comes around. I used a shock collar twice with the dead chicken lying on the ground. That is what worked for me, but every dog is different.