If your going to cull the pups let them nurse some first , if not you have a good chance of messing up hormones.
I gave my gyp a shot for $28 at the vet, if you wait more than a day the shot they give is around $100 and its basicaly a morning after pill that worked great for my gyp
How will not letting them nurse mess with her hormones?? No different than if the gyp had pups and killed them as soon as they are born.. Part of mother nature if you ask me. I have also culled on the DOB and bred the gyp again later with no problems.