Whatever's the matter with Pie is still there, lurking under the surface. This evening, he was in his stall eating hay - it's horribly cold, windy (wind chills in the 30sF) and rainy out, so he's inside for the night - when he stopped eating and started looking uncomfortable - ears pinned, kicking at his belly and threatening to lie down. Same thing - a little too much hay too fast - and same result - abdominal discomfort. When I got to the barn in response to a call by our p.m. barn lady, he was just about to lie down - I had him stay up, got his halter on and we marched up and down the barn aisle for a while. His gums looked fine and he had pooped plenty. He was pretty alert and responsive and we said hello to a number of the other horses who were in their stalls. I also tied him up and groomed him - he seems to appreciate having his back and hindquarters curried and rubbed when he's uncomfortable. Then more walking. He started showing interest in hay again, so I put him in his stall with no hay - he pooped and seemed to be more comfortable and was very alert and interactive - and left him there for a while - turned off the lights and sat in the office. He was completely alert and hungry when I came back to check on him a while later. I gave him only a little bit more hay for the night.
I think being in the stall contributed to the problem - he seems to benefit from being able to move around in his paddock as it helps the gas move on through. I didn't really think that whatever it is that's wrong had just gone away - it's clearly still there although I think we can manage it for now by being careful with how much hay we feed him how quickly, and making sure to arrange for him to keep moving as much as possible. Just keeping my fingers crossed every day that he'll be OK . . .