Sorry, fly bites (or midges), and he's reacting to them -- developing oozy swellings which crust over.
I treat with a cream from vet, he has a fly rug, eats loadsa garlic but the buggers still go for him down there. Driving him mad!
I once saw a US site selling bands impregnated with fly-deterrent that you could wrap around the pasterns... if you had a fine-boned thoroughbred that is. Mine is more in the heavy hunter size category and the bands are too short.
(Also he frequently itches his face against that part of his leg, so I would worry that he might transfer harsh ingredients onto his nose/eyes.)
Anyone have any ideas? Thanks so much if you do! Live in France btw
We've got tons of buttercups this year but luckily have never had any trouble with them. Meanwhile the top half of our field is a no-go area in the summer because of wild parsnip (several sprayings but still can't kill it). That is terrible stuff for causing burns on muzzles and white legs.