My 11 year old shetland has very healthy hind feet but his fore feet aren't so good. The white line looks a little stretched in places (like grapefruit flesh) & there are a few small holes in it where grit from the road gets trapped. Of course I carefully remove all this grit. My farrier isn't concerned about it & says the pony doesn't need shoes. He also says he could put putty in the holes but bits of grit would get stuck to that. Anyway he's not keen to fill the holes because the putty could trap any infection that might be developing. I don't think his diet is the problem. If it was then I assume all 4 feet would be affected. I've fed molasses free healthy hooves all winter as well as hay.He's not significantly overweight & normally loses several kilos at the end of March/early April before the grass start to grow. A horsey friend has suggested it could be genetic so there isn't much I can do about it. Does anyone else have this problem?
She's a 4year old connemara and has had the problem for around 8 month on and off. 1st sign of it was a deep hoof abscess which turned out just as you say to be caused by grit in tiny holes/cavities in the white line. The abscess was treated and I was packing the cavity with cotton wool soaked in antiseptic. The cavity practically closed up but then went on to form of the other side of the hoof. Again I was packing it and doing as you say cleaning out all the tiny bits I could find. In the end I had to give in and get her shoed as she was sometimes a bit footy although not lame, I didn't plan to shoe her at this young age as she's still green and unpredictable if the wind blows the wrong way. 
