Took my goats for CAE testing last week (left a bit too late as usual) and while there I asked about this very thing. the goat was limping slightly and I'd started to trim wall right back but chickened out, worried I was overtrimming. Vet said the obvious, I had been doing right, if I didn't trim the wall right up, just more and more dirt would be forced up into the cavity, making it worse. I'd used a plastic scrubbing brush, but that didn't get far enough up the gap.
There is a thread somewhere which mentions copper, depending on whether you're on copper deficient land I believe even sheep need some? (hope sheep keepers will come back about this).