I have felt your pain and anger. I lost a whole flock to a pack of stray dogs / coyotes (could see the tracks in the mud) that dug under the fence during a very wet time of year. They left most of my dead chickens laying all around and only took a couple. It seems very strange to lose 50 all at once. That is a lot for dogs / coyotes to eat and carry off. Don't let this kill your desire to rasie the animals that you love and bring some happiness too you. Once the emotion dies down you can rebuild your flock. Goodluck finding the culprits whether four legged or two!!!