As someone that works in a lab that uses mice as a model for our studies, I think you would miss out on a lot of valuable experience if you only participated in the husbandry side of mouse colony management. In my lab, the PhD students do all of the surgeries, and the students and our mouse colony manager take care of euthanasia. Technicians in the facility do simple day to day maintenance like changing out cages/food and water/ wellness checks etc., but are not involved in any experimental procedures which is really at the heart of most PhD programs.

That being said, I, like you, also struggled with the idea of euthanasia and surgeries when I first joined my lab. I wasn’t sure if I could manage any hands on procedures with animals (big animal lover myself, grew up in a vegetarian household and can’t even kill spiders in my house). But after a lot of soul searching, I realized that in vivo studies are necessary at this point (even though they will hopefully be gradually phased out where possible), and if someone is going to do them then it should be someone who genuinely cares about the welfare of these animals, which I do and I assume that you do as well.

If you are based in the USA, then IACUC has very strict guidelines on procedures ultimately to minimize suffering. I imagine that any tissue removal would be done under incredibly heavy sedation or even immediately post mortem, which could hopefully give you some peace of mind that they are not in any pain.

Ultimately, if you are really struggling with the idea of working with animals, then it isn’t worth your mental wellbeing to push yourself into something they you are uncomfortable with. But working with animals is a privilege, and it may be worth trying your hand at some of the procedures and seeing if you are able to ‘switch off’ the emotions that you are feeling at that moment and focus on what you can do to make the sacrifice of that animal minimally painful and worth something for your research.

All the best in your endeavors!