For what its worth I agree with the others who say that these animals have probably had enough...let them go. For me it is the ULTIMATE mark of love and respect for our animals to be generous, considerate and brave enough (and it is very hard) to say a timely goodbye, ie before the animal has deteriorated to an undignified and painful condition.
Ask the owners to consider how they would feel if they were in that condition themselves. As a nurse I know when people have had enough of life...often they will express that....sadly animals cant. In the wild they would take themselves off to a quiet place for a quick and dignified death...we are the ones who keep them 'in public view' and stuff them full of medical chemicals, creating an artificial extention to their lives.
I know it is hard, so very hard...I have sobbed my heart out, lying in the field beside beloved horses and ponies as the final anaesthetic takes effect, or cradling my treasured dogs in my arms as life quietly leaves them. But those moments, memories of which bring tears to my eyes as I type, are the final step in a shared journey and the final act of love.
Please pass on heartfelt sadness for the hard decision your friends have to make. But it is the right one.
Emma