I'm quite sure it wouldn't hurt them at all. I'll have to do some research and see what I can find, but I'll be an excess of copper (or some other mineral/metal) will prevent ovulation. Maybe I can find something by researching infertility.
Thanks for passing this along, cool information to know - especially if it's not toxic, not lasting. Perfect for show season then, don't you think?
Interesting thing about old remedies. Are they myths or things that work? As far back as the Old Testament they were putting objects in animals water troughs . The glass ball sounds like the body tricked into thinking it's pregnant though.