At some point you may have to make the hardest decision you have ever made regarding your pet's welfare. Your pet may have a severe injury, a painful disability, an incurable illness or another life debilitating condition, at this point putting your pet to sleep, or euthanasia, may be the best option for your pet. If your pet's quality of life is such that it can no longer enjoy life as it once had then the kindest thing you can do is to have it put to sleep.
This can, and is, a very difficult decision to make and every case is different, your veterinary surgeon will be able to give you all the help that you will need to make sure you have made the right decision. It can be selfish and cruel to make your pet continue to exist if it is suffering in any way.
Euthanasia is an overdose of barbiturates given by intravenous injection, if possible, and administered by your veterinary surgeon with your consent. You will probably have to sign a form giving your permission for this procedure to be carried out. You will be more than welcome to stay with your pet while it is put to sleep. It helps some people to know that their pet slipped away quickly and quietly and they could be with them to comfort them in their last moments.
If possible try to discuss with your vet beforehand what will happen to the body afterwards. There are various things that can be done with the body, such as, taking the body home to bury it, leaving the pet at the surgery, burial at a pet cemetery, or it can be cremated. When you leave the pet at the surgery it would be routinely cremated either on the premises or at a pet crematorium. Pet cemeteries need a few days notice before you would be able to bury your pet, your vet could probably help by allowing you to leave the body at the surgery till the cemetery was ready for the burial. Pet crematoriums can allow you to have your pet cremated on its own and you will get the ashes back, some owners scatter these ashes in their pet's favourite place in the garden.
Euthanasia brings about a peaceful end and you will know that after all the years of caring you have done the honorable thing for your pet.