It’s important to differentiate between metabolic laminitis and mechanically-induced laminitis.
If the horse is not demonstrating any other signs of metabolic issues and is just demonstrating soreness and foot pain, especially if it’s only right after being trimmed, I wouldn’t necessarily jump right to metabolic laminitis. Low heels by itself is not a sign of metabolic laminitis or metabolic-related foot issues. But low heels can be a sign of foot balance issues.
Could you post some pictures of his feet on flat, level ground? It may be that he was being trimmed poorly, or maybe trimmed in a way the farrier thought was correct but for the horse’s needs was not. Bruising in that area indicates either A) the horse is landing toe first, and the constant concussion on the toe is causing some bruising and possibly some mechanically-induced separation of the laminae, or B) the horse’s toes are too long and there is undue tearing-type pressure when the horse moves. Proper trimming or shoeing would fix this, whereas diet changes would not.
Is this new farrier the same one that’s been trimming the horse the last two cycles when he’s been lame?
ETA: OP, have you or the farrier or a vet actually hoof tested the horse? If so, where has he shown up sore? If the horse has low heels, he could be developing caudal heel pain and compensating by landing toe first - so the toe bruising may be just another symptom and not actually the real issue.
