The most effective supplement? It's what's NOT in it that makes it better. No iron. Iron and its partner in crime...manganese.
Many labels won't list the iron content on the analysis. What you don't know won't hurt you...but you're not eating it, the horse is. If you see words like ferrous, calcium phosphate, sulphur or high manganese, know also the iron is high.
Part of my homework in nutrition class was to find a supplement that complimented our individual hay tests. Since iron wasn't on analysis for Farrier's Formula, (and this was years ago before the double strength came out) I called them to ask them how much iron was in it. They wouldn't tell me. So I sent some to a lab to get it tested and it came back with a disgusting amount of iron in it. No wonder they wouldn't tell me! I don't recommend it anymore.
Iron is a real baddie to a horse. Iron deletes the uptake of copper and zinc, which is very important for good hoof health. The little bit of copper and zinc that are in FF have no chance with the iron that is being delivered with it....waste of money. If you wish to feed biotin, then feed biotin. You can get pure biotin at Uckele. You can also get a higher and more effective amount of copper and zinc and no iron and the same biotin with California Trace minerals.
I will post both links so that you can compare them yourself. The California Trace website also has a handy calculator there.
Farrier's Formula
Farrier's Formula Double Strength Nutrition Information
California Trace
California Trace - Nutritional Support for Horses
If you wish to know just how bad iron is, just google "iron overload in horses"
Just food for thought. I know you guys are seeing the results of the biotin and it can take up to 7 months to see a difference. Biotin is a B vitamin, no more, no less and just a small part of the nutrition that is needed for healthy hooves. The trace minerals are far more important and with no iron added to the California Trace, you get sufficient copper and zinc to fight the iron that's in the rest of his daily intake, instead of increasing iron/deleting copper and zinc with Farrier's Formula all by itself. Its all about balance. Geez! Big imbalance with calcium and phosphorus as well! Not good either!
Hope this helps.....