You need to make sure your dog never gets loose again so it does not get into that situation again. You need to talk with the livestock owner and offer to pay for damages if the livestock was killed or if the attack causes veterinary expense to the owner. I do not know where you live but in our state a livestock owner has the right to shoot and kill any dog that is either chasing or attacking their livestock. You as the owner would be responsible for your dog being killed since you allowed it into the situation.