Hair shedding only around hoofs?

I have recently acquired a 20 year old horse that had been turned out to pasture for a year or so. Everything was going good the last 6 months getting him back in shape slowly gaining a little weight and muscle. I did have the vet out for a physical and was told all was well and recommended he be but on a senior complete feed with a soy base and add soy oil for supplement. He is eating high quality grass hay and a flake of alfalfa grass mix.
The problem I though the hair on his legs, down around the hoof was shedding but the vet and his farrier did not think what I was pointing out was a problem, which maybe it isn’t? Its not falling out in clumps just thinner and shorter above the hoof, on all four legs. Yesterday his back fetlock was slightly swollen with no heat, and he was a little off on that leg. He looks better today swelling has gone down a bit, its not soft or hot, he is still off a little but better. The hair on that leg from the hoofline up is now noticeable shorter and in reaches up to the fetlock, in spots. I called the vet he didn’t seem worried and told me to keep an eye on it and call him in a few days.
I have never seen this before, why is his hair shedding out only around his hooves? I’m really starting to think something is wrong. Advise, thoughts?
I lean towards being a hypochondriac when it comes to my horses but the vet is not worried.
What is going on?

My horse recently lost hair also around his hooves, it was due to the soft field conditions, I used hibi scrub for a few days with some flamazine incase of underlying mud rash, seems ok now could be worth a try