Gertie is done every 4 weeks due to a nasty injury, previously was every 5 weeks. Monty will go months and months without needing them doing although they do get checked when the farrier comes to see my little mare, just incase.
My retired gelding has his done every other time the girls are shod, so roughly 12 weeks, he doesn't seem to get much growth and we have to bute him up the night before as he struggles to stand with 1 leg up, arthuritis (sp).
Cobbie and welshie...varies from 12 weeks to 6 months
Mini Shettie... every six months or so
Shettie(6) and Exmoor cross(4)... never been done..perfect lttle feet