Your horse is most likely suffering from a hoof abscess within his sole. Abscesses usually come on very quickly, and can cause swelling up into and past the fetlock. An abscess is formed by bacteria entering through a tiny crack within the sole/white line, and once the hole seals, the bacteria begins to multiply forming a large pus pocket. This causes an incredible amount of pain within the foot, preventing your horse from applying any weight on the leg. Your horse needs to be seen by a vet, so the abscess can be located and drained. Your vet will use a special tool called a hoof tester, which gives an approximate location of the abscess by applying mild pressure to various parts of the sole. Once the abscess is located, a small hole is made into the abscess, allowing it to drain. I will usually pack the hole with cotton-soaked betadine, followed with a duct tape bandage. Healing normally takes about 1-2 weeks, depending on the size of the abscess. Your vet will also need to boost your horse's tetanus vaccine, if he has not had one within the past year.
While you are waiting for the vet to arrive, I would recommend soaking his hoof in a combination of warm water, epsom salts (1 cup per gallon) and a small amount of betadine so the solution resembles very weak tea. Soak for 20 minutes or so, or as long as he will allow it. If you have any sheet cotton, or thick, soft fabric, it may help to duct tape this to the bottom of his hoof, but be sure that the duct tape stays only on the hoof wall and not the coronet band. Soft bedding will also help.
Antibiotics are normally not necessary for hoof abscesses, as the infection is localized and can not spread to different parts of the body.
As far as the nasal discharge, there is a possibility that he has sustained some type of minor head trauma as there are multiple capillariues within the sinuses that can bleed easily with little distubance. I could also not rule out the possibility of an upper respiratory tract or gutteral pouch infection, especially since the discharge is only being seen from one side of his nose. It would certainly be worth your while to have your vet address this issue as well, while the abscess is being tended to.
I hope this had helped, and please let me know if you have further questions.
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