Okay: a few good rides in a row again, though I'm off for a work trip for the next few days out of state, alas.
Thought I'd record for posterity a few small changes to Tristan's routine.
The first is that I'm feeding him 8 Tums (the generic Walmart version) about 15-20 minutes before every ride. I'm only three rides into this. It's an experiment. He's never struck me as an ulcery horse, really - he's pretty chill - but he does get very head-flippy and resistant during warmup. Now, part of this is definitely my lack of riding ability - but part of it is unwillingness. I'm not ready to report back yet, but early indications are a slight positive. (If nothing else, he eats them like candy and that puts him in a good mood...)
I consulted with my vet and took him off Previcoxx. He'd been on it since shortly after his surgery (basically week 2 of rehab, when he stepped down off bute), more as a general anti-inflammatory than in response to anything specific. I was being extra-cautious in keeping him on it daily, and it was inexpensive and provided by the barn (~$20 a month). When I weighed the longterm liver problems of a daily NSAID (eek) with his age (not quite old enough to prioritize comfort over longevity) and the probable benefit he was getting (possibly nil), vet agreed that we should pull it.
He still gets a daily joint supplement - HorseTech's ReitSport Senior - and the vet and I are going to revisit the general support question as he progresses in work off the Previcoxx. I may do a round or two of Adequan/Pentosan with him when they come back on the market. It's not pressing right now, but it's something I'd like to try. If it does make a big difference I'd ratchet back his oral supplement to just a mutlivitamin/probiotic and keep up the injectables regularly.
Finally, a few days ago I caught him eating his manure. Corprophagy, for him, is a very reliable indicator that he needs a salt block. Several months ago he had a biiiiig red one in his stall on the ground and he'd been using that, but it vanished when he shifted stalls and I have been too darn lazy to seek it out again. So I picked a little one up at Tractor Supply, dropped it in his feed bucket, and he has been licking away since, happy as a clam. (Alas, he destroys the wall-mounted holders with distressing regularity, leaving me to panic about screws falling into his bedding and/or projecting metal pieces jabbing his eye.)
So there's that. His weight is inching up again as his grain has been upped - he's getting a whole half quart in his AM and PM feed, the glutton. I toyed with the idea of switching him to a senior feed recently but after reading and comparing labels they didn't address anything he particularly needed - he's not a hard keeper and he's in very good overall health and doesn't need the kind of support they tend to provide. Someday, but not today.