[Fluivelip]

The precepts are to guide and are not hard and fast rules. I would suggest you act for the greater good and only you can decide what that is. If you are helping animals out of suffering that were going to die in pain otherwise then I would think you are acting for the greater good. If you have to do this with healthy animals that are not in pain it may be a more difficult question but are you acting for the greater good if you lose your job and can't support yourself/family?. If you don't look after yourself you will not be able to look after others.
One other thing comes to mind, If you don't work there then the same animals will still be there and still be euthanised, they are not saved by you not working there but you could be playing an important role by staying in the job and ensuring that the animals are treated well.
If you left the job and then and a less caring person took your position, what have you achieved?
I hope this is of some help to you