I never really thought about pets needing blood, until I started following Dr. Jean Dodds DVM. She is quoted in the article:
California requires closed colonies, and Jean Dodds, the founder of Hemopet, a nonprofit commercial blood bank there, is adamant that it is the best way to ensure the safety of blood products and a regular supply. Hemopet's website shows dogs resting in crates in brightly colored "bungalows" alongside a courtyard used for daily walks. It houses about 200 greyhounds that, depending on their weight, donate twice or three times a month before being made available for adoption after no more than one year, Dodds said.