My horses frogs has split on his forefeet!?

at first i thought it was thrush, but my friend said it would smell and have black goo in it! its now split right up the bulb of his heel to his coronet band, he doest seem in pain but flinches when i clean it out! the field he is in is very muddy and wet around gate where he stands alot and he has mudfever on his hind feet! should i be worried? what is it? and how can i get rid of it? putting him in a different field isnt really an option as there all muddy and wet by the gates!