1. AAHA 2005 Senior Care Guidelines for Dogs and Cats https://www.aaha.org/professional/resources/senior_care.aspx
2. AHA 2016 Euthanasia: making the decision American Humane Association http://www.americanhumane.org/fact-sheet/euthanasia-making-the-decision/
3. AVMA 2012 U.S. Pet Ownership and Demographics Sourcebook https://www.avma.org/kb/resources/statistics/pages/market-research-statistics-us-pet-ownership-demographics-sourcebook.aspx
4. Hellyer , P. W. Uhrig , S. R. Robinson , N. G. 2006 Colorado State University, Veterinary Medical Center, Canine Acute Pain Scale v.2 http://www.vasg.org/pdfs/CSU_Acute_Pain_Scale_Canine.pdf
5. PetPlace 2015 When is a dog considered senior? http://www.petplace.com/article/dogs/keeping-your-dog-healthy/senior-dog-care/when-is-a-dog-considered-senior