There is a birth defect that can happen to horses, though is very rare. There is a band that is by the heart that closes off their esophagus, just before the foal is born that band is supposed to release.
I had a beautiful buckskin Windchaser son, who started choke when he was 9 days old, it cleared up and he had it again at 12 days old and I could not get it to clear up. He would not nurse his mom either. He started to crash so I brought him up to the vets and the vet felt that this was what his problem was. They tried to tube him and could not get the smallest of tubes down him. They brough him back to normal, but he continued to choke then go off nursing. I had the vets work with him for two days, but I finially had to put him down. My vet did a necropsy and that was what it was. He said is is very rare and you see one in about every 30 years.
Your colt must have still had the band, but it was open enough for him to get food. But, with his growning, it finially started to choke his food supply off.
Oh no poor Eddie! I know you have done everything you possibly could for him. He was always such a tiny little guy. By the time u got him he really had barely grown much at all, I thought he was just going to be tiny. Sounds like its something no one could have known about or corrected.
I would like to offer you a replacement colt. I have 2 lovely black colts born this year and if u would like one u are welcome to pick one out. They are not brothers to Eddie as his dam had her uterus prolapse this year and vet. said not to breed her again. Jen