1. What works for my horses hooves that has the vet and the Trimmers commenting (without prompting) how great all their hooves are:
Omega-3 Horseshine. Yes a bag is expensive but I feed it to three horses and 20 lbs lasts me five weeks. You can get it at Tractor Supply. They have their own knock-off brand for a lot less money but I won't use it; maybe there's no difference, maybe there is but I'm still not using it Best natural horse supplement and treats with stabilized flax for joint, hoof and skin coat health
2. For a totally different reason, I put my A.D.D. TWH on AniMed's "Remission". It is mainly magnesium but does have probiotics in it.
To my great surprise, the Remission has really calmed him down. So-much-so that the Arab has, after 16 years together, finally let the A.D.D. Guy do the itchy thing once in awhile.
I feed it to two horses; I haven't dated a tub but I think 4 lbs lasts 4 - 5 weeks. I pay $23 at the feed store.
Remission is cheap and lasts a long time. I have found it at two hometown feed stores or you can order it on-line. AniMed Remission - Horse.com
3. Also if you're feeding sweet feed, that's a great way to amp the horse up and maybe even make her heat cycle worse.
My A.D.D. Horse is also oat/corn/soy intolerant. Removing those things from his diet helped immensely but when I added the Remission, the change was phenominal. He's got allergies too. I haven't had to feed him his allergy herbs since I started him on the Remission
Hope this helps