Euthanasia and the Animal Shelter
http://www.api4animals.org/articles?p=352&more=1
The euthanasia method of choice for use in animal shelters is the injection of an overdose of a barbiturate anesthetic called sodium pentobarbital. In API's view, it is the only acceptable method of euthanizing shelter animals. When injected into a vein, this drug produces rapid unconsciousness and death without the pain and distress that accompany all other methods.