I'm not sure, but I think it could be a little risky, I was recomended not to feed to a lactating mare but wait till the foal was weaned. I'm not sure exactly why though, something to do with the imbalance of calcium or something? just a guess?
Sorry can't be of more help.
can i ask what you feed it fr and is it really necessary?
Ive just phoned up the provider of Bloss's herbal pollen allergy suppliment to see if i can feed it to her during pregnancy and its fine - but im only feeding her that as she HAS to have it due to her allergy.