It is fairly common for horses to step on nails and have the nail puncture the foot. So if you notice your horse limping, pick up the foot and find a nail, what should you do? Most people would just pull the nail out and not worry about it. Well, both of those answers are wrong. It is important to leave the object in the horse's foot until the vet arrives so x-rays can be taken to see what structures the nail may have entered. If the horse is really lame and the nail is sticking below the sole, you do not want the horse stepping on it to drive it any deeper so you may have to pull it out. If you must remove it, mark the entry spot so your vet can find it and check the direction because a probe will need to be placed in the hole and the area x-rayed. If possible, leave the object in the foot but cut it off so it will not be pushed further in the foot and wrap the foot with loose cotton to pad and protect it until the vet arrives.
A nail or other object that enters the horse's foot can be extremely serious and even deadly. The reason is if the nail has entered a joint or tendon sheath and causes an infection, the infection can be difficult to cure - sometimes impossible. Some of these horses are in such pain due to infection in the area that euthanasia may be required so that is the reason I say a nail in the foot can be deadly. So if you find that a nail or other object has punctured the sole of your horse's foot, don't just pull it out but call your vet and ask for advice. And these infections may take a day or two to become painful from infection so even if you do pull out the nail and your horse appears normal, this does not mean a problem will not develop. If you wait until your horse becomes lame, it may be too late.
It is also important to make sure your horse is up to date on tetanus vaccine if any type of wound occurs. Tetanus vaccines should be given annually to all horses.