Horses evolved for pretty dry, hard conditions, and I do believe those are the conditions that are best suited to them. But mud *in moderation* is not harmful. It's when they're stuck in nothing but mud or a waterlogged paddock all the time that's the big prob. If he only walks thru the mud a couple of times a day but is otherwise on firm, dry(ish) ground, that's likely fine.
BUT even if his feet are healthy, they will be softer & weaker for living on soft, damp ground, so will likely need some protection when made to go on hard ground they're not 'conditioned' for. Bit like, if you're used to going barefoot only on the carpet at home, on the occasions you tried to go bare on the gravel outside, you'd likely feel the need of some protection!
The more exercise on firm, dry ground the better(so long as he's able to be made comfortable doing it).
Soft, muddy ground can also encourage contraction through lack of good stimulation to the back of the foot, lack of good hoof function. It can also be a great encouragement for infections such as thrush to take hold.
Are there any products/methods I can use to ensure my horse's good hoof health?
I disagree with the use of topical hoof goop *generally*. The only products that will really help this particular issue is treating the hooves regularly to avoid/treat infection, and boots or some such to protect the feet when you need the horse to cope on hard footing.
He is on Biotin supplements (10mg/day), feet are picked about every-other day, regular trims (7-8 weeks), and has thrush treatment applied after each trim (farrier recommended). ....
Next, we were at a different barn with small (dry) gravel paddocks. My horse's feet got very hard and chipped a LOT!
Good that he's on biotin, if he's not getting enough green pick. If he is, then he may be getting enough in his diet so supping it is unnecessary. Excess biotin is not harmful, just a waste tho. Most domestic horses(depending on grazing/hay etc) are deficient or imbalanced in a heap of different nutrients tho, so IMO a *good* complete supp is a good idea, as is at least a basic diet/feed analysis to work out what exactly they need. Nutrition-wise, the hooves & hair are the extremities that reflect the whole body, so I don't tend to go for specific 'hoof supps'.
7-8 weekly trims are generally too long for most horses, altho it depends on many factors & some can healthily be left that long. 4-5 weeks seems to be a generally healthy schedule for the majority of horses. If a horse's feet are to be made/kept sound & strong, then they need to be trimmed frequently enough to *keep* them in shape, rather than waiting for them to become overgrown & then fix it. Being left too long &/or not being trimmed well is the general reason for chipping, altho other factors, such as diet, infection, soft feet, separation, etc will come into it too.
Regarding thrush treatments, if the horse has thrush, once a week treatment is unlikely to help much, let alone once every 7-8 weeks. It needs doing at least daily. If the horse doesn't have thrush, then there is no point in treating it, altho spraying the hooves daily with ACV or such will help it being kept at bay, as it doesn't like acid environments. If a horse is receiving well balanced nutrition, it will be less susceptible to infections such as thrush. Also it seems that it is strongly related to hoof function, and the more exercise & better used the back of the hoof, the less likely it is to develop thrush, even in environments that the bacteria thrive in. Therefore it's possible that it's not the mud itself that is the cause of thrush, but the lack of hoof function & subsequent contraction & weakening of the heels that leads to it.
So, we're back to a barn with mud in its pastures, but now have a very hard, dirt arena.
Personally I'd jump at a dry, gravelly environment, to strengthen, condition & support my horse's hooves. I had very little difficulty rehabbing & 'transitioning' horses to barefoot when we were in that environment, but ATM, I'm in your situation - soft, reasonably soggy pasture, but only hard, gravelly tracks & roads to ride on. So I'm finding these days, my horses generally need hoof boots when going out. Come on summer!