Do you think mares that have had foals are different than ones that never do?

I've heard about that wives tale too, but I don't know. I'm breeding my barrel mare when she gets older, but I don't think she could possibly get any calmer than she already is. I haven't noticed any difference though - we had a mare that was bred before we got her and she was hyped up, spooky, and just crazy pretty much. So probably not.