Two vets are working on this and both aren't sure what could be causing this. Colic and Founder have been ruled out. The only change in the horses diet is that he went from getting flakes of hay in the PM to getting cubes due to shortage.
Owner wasn't present when the horse went down the first time so we can't be positive that it isn't an injury. Vets have used every method possible to get him to his feet and haven't been successful.
Most importantly, say a prayer. This is a sweet, gentle giant with a heart of gold. His owner adores him and will do anything to have him better.
Secondly, if you have any ideas or similar experiences, we'd love to hear it.