Very sorry to hear about your dog, i have a jack russell who is 3 but his brother got knocked over by a trator when he was just 1.We do our best to look after them and then something like this happens.I had a cat 6 years it was only the 2nd time it had been left out all night and she got knocked over and after a £350 vet bill she had to be put down she was our first pet, but you do start to get over it in time, times a great healer.