It may surprise you to learn that birds, rats, and mice are no longer considered animals, but that is the sort of logic that epitomizes federal legislators. Researchers are not allowed to abuse animals, so the definition of animal is simply revised until it refers only to creatures researchers don't need. Garet Lahvis, a behavioral neuroscientist at Oregon Health & Science University in Portland, correctly notes, "We study animals to see what makes us uniquely human, but the findings of empathy in animals often force uncomfortable questions about how humans treat animals."
The animals care about how they are treated and we also should and must
So, it just may be that years ago researchers and those people responsible for developing legislation and guidelines for the use of animals in research were actually more humane. Although many people who studied and shared their homes with rodents and other animals knew they were sentient beings, the scientific evidence wasn't available and those who used animals or favored their use could say and get away with something like, "We don't know if these animals are sentient or emotional so until we do we can do whatever we want to them." Some researchers still act as if this were true, but now the data are available and they have been published in highly prestigious peer-reviewed scientific journals and it boggles my mind that researchers continue to use these animals as if they -- the animals -- also don't care about how they were treated. They do, and we also should and must.