Natural Remedies to Help Heal Horse Wounds

I need help with a wound on my horses front leg, just above the knee. Wound was sutured but previous owner removed pressure wrap and sutures busted out and the owner just left it to rot. I have gotten rid of all the proud flesh, and have gone from the size of a cantalope to a small hole about the size of dime, but it is a hole all the way thru the skin. Vet tried to cast so that it would heal and that was a complete disaster! I am treating it with an Equi Stim machine (micro current) with great results, just need that last little bit that is so hard to get!! Thanks in advance for your help! Oh, I am spraying the wound with calendula oil mixed with distilled water.