Where do animals go after being put down at a vets?

This will depend upon the owner's wishes, the local laws and the specific animal. A number of owners will elect to take their pet home to be buried, particularly among small animal owners. Other small animals will be cremated at the owner's expense; the ashes are typically returned to their owners. If the remains are left with the veterinarian, they are typically either disposed of through the local landfill or through a biohazard collection service.

Large animals may be buried on site, picked up by a rendering facility, or disposed of in the local landfill.
They give you a choice to keep the pet, barry it, or have it cremeated. If you do not tell them specifically they will cremeate your pet and have the ashes sent to you.