Any hoof wall crack needs evaluation of foot balance, non-hemorrhaging horn removal that is creating pressure, supportive shoeing and re-check until there is no longer any crack showing at the growing coronet.
Causes of cracks in horses:
Trauma to the coronet (usually unilateral)
Too much exposure to wet pasture and/or mud
Too much exposure to fescue pasture
Irregular shoeing or trimming intervals
Allowing flaring of the toes and walls to occur
Owners should manage the hoof environment before any hoof or shoeing alterations. If hoof management doesn't change, hoof treatments can not be successful.
The horse should be maintained in as dry an environment as possible. No turnout during wet times. Off dew wet pasture. Consider a clean pine shavings stall as primary "home", turnout in late afternoon and in about 10PM and then could turnout about 8AM for a few hours. Fescue pasture maybe a hindrance to decent hoof health.
A packed sand, small paddock can be a turnout area for such a horse in wet times.
Make sure hay is fed on a platform that can be swept to avoid sand colic.
Encourage daily exercise whether ground or ridden exercising to help maintain health.
Keep weight reasonable with a body score no greater than 6.
Consider as much heel support as the farrier dares.
Consider adding frog support.
Consider at least setting the shoe back to a straight line drawn from the top 1/3 of hoof to the baring surface (see photo below).
Consider setting break-over back from that point.
Without causing any blood, relieve the firm horn from both sides of the cracks in a V-shape. The long point of V is about 3/8 to 1/2" on either side of the crack along the coronet (see photo above, right).
Goal: To shave off horn to a point just below the crack line and have no crack at the coronet. It may take 2 or 3 "shavings", 1 to 2 weeks apart to accomplish. If you do get a bead of blood or more, wrap for one day with aqueous based antibiotic cream.
Re-check site each shoeing to pare away any abnormal hard horn.
Keep lanolin based hoof ointment rubbed into coronet band to keep coronet soft.
No caustic treatments!! That only makes a heavier scar.