My 11 YO appendix has notoriously bad feet and for months now we have been combating white line separation. He wears front shoes and the separation is only in his front right foot.
Yep, separation/seedy toe/WLD tends to be a common symptom of 'notoriously bad feet'. There's generally more to it than 'just' seedy toe infection - generally bad mechanics are at the route, which allow the feet to become separated & then get infected. While it can be really difficult if the horse is in a bad environment, and keeping the horse shod can make it(& the mechanics that allowed it) harder to treat, if you've been battling already for months, to no avail, something's not right IME.
I called farrier and he said that its time for 'resection' , is that just taking more hoof wall off? How much wall can he safely take off? The horse is lame at the trot (in hand)
Is the horse actually lame because of the infection do you think? That's an indication that it's pretty severe & I would be very concerned that it's got to that point. If not treated effectively, infection can actually even eat into live tissue & bone. I would be involving a vet, if you haven't already. How long has he been lame & if not due to WLD, what has been the diagnosis?
Yes, unless the horse is in an ideal environment & the infection is very superficial, the owner very diligent with ongoing treatment, etc, I consider resecting generally necessary. As little as possible, but as much as necessary, to remove all infected material if possible(not if it goes into live tissue though). It's an insidious disease that can eat away at healthy tissue quicker than it can grow & gets in deep, so it's not able to be treated topically without being cleaned out. I would have done this to begin with, not leave it until the problem became worse.
As for how much, you can take away most of the hoof wall if necessary. That is only needed in really severe cases. Obviously if so, the horse couldn't be shod(I wouldn't have him shod until this is treated anyway) and would need protection from bashing his foot, with the sensitive corium so close to the surface. Generally only relatively small areas need to be removed & if the resect goes more than half way up the wall a brace across the face of the cut may be needed.
The hoof wall is par of the wall that the horse stands on. The more you take the more you need to support.
The hoof shouldn't be peripherally loaded - bearing most of the weight on hoof walls, and this is one common reason for stretching/separation, and the biggest reason I'd be avoiding conventional rims, at least until his feet were healthy.
As a side note, my farrier had mentioned to me that the worst thing you would do for WLD is to try and treat it with chemicals intended for thrush.
Thrush & WLD/seedy are basically the same sort of infection in different parts of the foot. Therefore the same antiseptics should kill both. **So long as** it is not applied anywhere near sensitive tissue, it shouldn't be problematic to use heavy duty chemicals on hoof wall infection. So saying, I wouldn't let something like formaldehyde or bleach anywhere near a seriously resected hoof - it's usually far too close to live tissue that it can damage. But I don't like to use anything harsh on frogs, particularly in the central sulcus, where there is so much sensitive tissue, sensory perceptors, etc. So... I'd potentially use something like thrushbuster on WLD but not thrush.
And it will not hurt him to be walking on this 'jacked up' foot because he is wearing shoes which holds his weight , correct?
Also , what would you suggest using on his foot to kill the infection ? Or nothing at all?
I don't understand why his hoof should be 'jacked up'? Yes, IME using conventional peripheral loading rims on a horse with stretched, separated walls & forcing those damaged walls to take the entire load is indeed going to do further harm. If the foot also needs substantial resecting, the wall that is left will also be under more strain, as there's less to spread the load.
There have been a few suggestions & you definitely need to treat it diligently - if he hasn't been treated in between farrier visits, then regardless of how good the farrier did, unless conditions are ideal, it will be pretty much untreatable. So, if after resecting there is a fair amount of hoof wall left, I'd attack it with something pretty heavy duty, but if it's into/close to sensitive tissue, I'd stick to something like diluted t-tree, salt, manuka honey, etc.