Probably caused by the dry weather. I use Kevin Bacon hoof grease on mine, which seems to keep them in reasonable order. Had horrible hooves last summer, much better this year!
Mine is barefoot and feet fine, living out so spending most of her time on nice soft grass!
Have to 'water her hooves' and then seal with Kevin Bacon hoof grease though otherwise she tips the water buckets out to make a nice wet patch to stand in!
Mine look a bit of a mess as they've got very chipped, but are actually functioning brilliantly (he's barefoot but doesn't get quite enough mileage really). Hacked out this morning over stone-strewn roads without his boots and he was stomping over it. They certainly looked prettier a month ago though.
Mine are all bare and on a bf diet but this last week/ 2 weeks has saw my 2 TBs feet turn awful, the other 3 non TB's are fine. Thought it might be something to do with this consistently dry weather.
Unfortunately stimulation is difficult when they aren't safe to take out, I'm getting a loan so I can put some sort of road/ track in the field but i need planning first. They have been ok condition wise before now, just suddenly started breaking off and splitting.
It does seem that the lack of stimulation is the problem - so given the temperaments of the horses involved, your solution (put surfaces down at the yard/field) seems like the best way forward. Fingers X'd that you get the planning permission.
Are they due for a trim sooner than normal? My lot had a bit of a rush on hoof growth the last month and I needed to get them trimmed sooner than expected.
That's possible, maybe they are growing faster than what I'm used to now they have better nutrition? They are booked in for trims but that might be another week or so before they get done.