Now I've actually read replies...
To the person who said that the hooves can't grow out too fast if trimmed every 6-8 weeks- that is simply not true. When I fed Whiskey farrier's formula, his hooves grew about 1 inch every 4 weeks.
I suspect there was something else going on there, because so far as I'm aware, even the healthiest bare endurance horses don't tend to grow that fast. Perhaps like shedding soles, which made hoof walls look extra long all of a sudden. Also, studies have shown that it would typically take 6-9 months before any real changes from supps *start* to occur, so interested to know how long you fed it?
Yes, certain conditions & supplements can indeed make hooves grow quicker, but I think what Natisha may have meant is that it's not 'too fast' or rather, it's not a bad thing that they grow fast. That they grew fast but shelly is another thing, that could have been due to nutrition, diet(as opposed to nutrition), management, etc.
Studies have shown that regardless of well balanced nutrition or other changes in care, biotin can make hooves grow quicker, but it doesn't necessarily effect how healthy they are. However, you need all
the ingredients in the right amounts to make a good
cake. Biotin is but one of many, which may or may not be deficient in a horse's diet. Many commercial supps that I've looked at(with the help of FeedXL.com, because I've found lables also often don't tell all) are not well balanced, for an average pasture/hay fed horse. It also depends what's in the feed as to what extra they need. Some commonly deficient ones that relate to the feet are copper, zinc, magnesium, iodine, methionine, omega 3s.
The outer layer of the(healthy) hoof wall is made of tightly packed, dead, dry tubules. As they are so tight and also (assuming diet/nutrition provides) they are coated in fats/wax naturally. This makes the outer horn pretty impervious to water & some topicals and keeps the moisture of the inner wall from escaping. This layer can however be damaged, esp. by astringent type chemicals (essential oils, paints, acetone, etc, etc) and then it can allow the hooves to dry out & crack. That is one reason I'd quit using cornescrine & wouldn't bother with other topical gunk. They are great at claims of 'miraculous hoof growth', 'healing cracks' etc, but IME & from studies I've read, all they're really good for is helping the hooves look a little prettier... when they don't make them look worse by stripping the protective layer & drying them out. Check out this link; The Horse | Hoof Dressings: What Studies Show
Assuming your horse's hooves weren't longer than they are in the 'after' pics & that's average growth, it looks like 6 weeks is too long for them to go between trimming, at least if he works on hard, flattish surfaces. I'd see how he goes with 4 weekly during summer & 6 max when growth slows & ground is more yielding in winter.