From the San Jose (CA) Mercury News, "Dog blood donations in California: Inhumane or saving lives?"
I know there are other veterinary blood banks that house and care for their feline blood donors in a similar manner, although I believe in those cases, the cats are not kept in cages but are free to run around in a large space with other cats. My understanding is also that- at least in the case of the organization with which I'm most familiar- the cats, who become extremely gentle and well-socialized after a year or so of blood donor activity, are then adopted out to new homes.
We make our facilities available to a blood bank in Colorado to come and collect donations from local dogs. They also offer yearly exams and blood work to their donors, which is necessary because those dogs are not kept in a controlled environment like the dogs in the article.
(If you think you and your pet might be interested in participating in a blood donation program, the criteria are below!)