"To euthanize a pet" means to painlessly end the life of a sick or suffering animal, usually done by a veterinarian, in order to prevent further suffering. Full definition
Not to be gross about it, but pet foods contain «meat meal», meaning it may also contain the bodies of euthanized pets. (thedogplace.org)
Some shelters are forced to humanely euthanize pets for health, age, behavior, lack of space, or other reasons. (humanesocietyofpinellas.org)
Many veterinarians are presented with cases where an owner is considered euthanizing their pet because of seemingly incurable behavioral problems. (smartdogowners.com)