Thanks, guys...he is doing better this morning. Once they got his stomach empty, he started improving. Vet seems cautiously optimistic that he won't need surgery (fingers crossed!). His colon seems to have moved back into its proper position. He'll stay there for the next week or so for observation and weaning back on to real food. I am very, very grateful that I live so close to an equine hospital!
p.s. He was such a good boy: last night was in the teens with single-digit windchill. He followed me right into a pitch-black trailer with freezing wind whipping snow sideways and making the trailer rattle and shake. I love this horse!