"He's had quite a few very loose poops, but has not been down and seems a lot better."

That's great news! Still keep an eye on him, since the Banamine may just be making him feel better.

BTW, I asked about the change in weather, earlier, b/c Baxter had a mild colic episode this winter when the temps went from the teens to the mid-60's. We were luckily already loading him into the trailer on our way to the university vet for a return visit for his back injury... The vet there was completely unconcerned and said that a sudden change in temperature/ air pressure can cause them to bloat and basically experience a colic-like episode (refused food, water; sweating etc.). Once he passed some manure and a bunch of gas, he was immediately back to his old self. I wonder if this was similar?

Ride smarter, not harder.