I'm sure the vet will send them to a medical waste disposal facility where they will probably be incinerated with the human bits and pieces from operations, friends of ours lost their dog and decided that they weren't going to get another,so they gathered up all the tins of food, basket, lead etc and took it to the dog rescue home to donate to them, they were shown round by a grateful member of staff, the only thing was they ended up having to ask for it all back for the dog that picked them while being shown round!