I use (funnily enough) "Worlds best hoof oil" and it really lives up to its name.
Two of my girls had a huge crack in one hoof so I put that on and it actually works really fast I was honestly suprised. And laasanna, arabian mare, white hooves, they are awful and she managed to take a big chunk out of one hoof god only knows how, but the hoof oil, applied daily worked wonders, and it leaves the hooves shiny to lol.
This stuff: World's Best Hoof Oil 500ml for sale - TradeMe.co.nz - New Zealand
And that advertising is not exagerated either it actually does work that well from my own experience.