Ok.. lovely question. I know too well about animal studies and soon enough, I will share one of my work using animal model.
For animals to be used for Such, ethical clearance must be obtained from Ethics committee in Such region. Before my research using animals, we always do this.
One thing you must not do is to kill the animal in a painful way (should the experiment require sacrificing the animal).
You must treat the animal as yourself. What you know will hurt you, you don't do to the animals.
They are always fed adequately and never starved. Good accomodation is also very important.
In summary, we just see them as little humans.
Empathy is the key word here.
Thanks for those highlights on these very important points. Cheers!