Since I also posted about what he is being fed on your other thread I will tell you founder or laminitis is a very good possibility. To me it sounds like that is a good fit. I would get the farrier out immediately along with the vet at the same time.
Edit: I copied this from your other thread.
What he is being fed right now: (which has slowly been introduced over time)
Unlimited access to fresh hay, fresh water & a protein salt block. Slowly being introduced to rich green grass.
Three times a day:
Two scoops of Dumor 14%.
1/4 scoop of Alfalfa pellets.
1/4 scoop of beet pulp.
A cup of Calf manna.
Farnam weight builder.
Once a day with his night feed:
A cup of corn oil.
Apple a day.
Sand clear (2nd week just to make sure all the sand is gone!)
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