[quasque]

The animals were bred specifically for such experiments. For example, the mice in these experiments were blind, immunosuppressed mice that would not survive in the wild anyway. Such research is not done with cruelty in mind; the animals are taken care of as well as possible despite their eventual fate - even their deaths are performed quickly and painlessly. In laboratory jargon, they are termed "sacrifices" which I think very positively describes their role - their lives being taken for the greater good of knowledge, enlightenment, and the overall reduction of suffering.