Is it sun poisoning or dew poisoning on a white mouth. This can become a problem where it was not one before. A new workout regime, perhaps more intense in the Australian heat. Look at the bit if this one is two yrs old. Has any coating come off, are there abrasions on the shanks or mouth piece.
Sharp cuts occur after long use and can be like a razor blade.
Usually though you will see evidence of this on the tongue and some throwing of the head. If it is a vitamin deficiency it would be B. A micro probiotic, Fast Trak or any reputable brand, would supply this along with the yeast cultures to rebalance the skin flora. Wound location and condition will be very important for your vet to know because location can determine the seriousness of the wound and how you should best proceed. You should also be on guard against any wound located below a hock or a knee or over a joint. This is a high-risk area and could have complications.