Finding Sources

I searched different combinations of  animal, euthanize and companion when I was looking for scholarly sources.  The most useful results were when I searched "companion animal euthanize." Most of the articles I found were about horses and rats. The articles about rats were talking about experiments where they used carbon to euthanize them. There were also debate type papers weighing the pros and cons of having to euthanize companion animals. Another debate was whether to treat or euthanize. When an animal gets a disease or gets hurt there is the question to euthanize or treat the animal for the existing condition. Although, my initial topic was about animals getting getting put down in shelters there wasn't very many articles about that specifically so I may have to gear my topic in a different direction. I was thinking about doing ways to prevent the illnesses and injuries that are cause for an animal to be euthanized. I haven't quite made a decision yet. There are also articles about the cost of such procedures. Whatever I choose I want to make sure there is more than enough information on the topic.