The question is what could cause such a thing. The foal was born alive and we milked the mare to get the colostrum into it etc. The vet said if we could keep it alive (which she doubted) for 24 hours then she might be able to do something for it. She also (the vet) said this was the third foal she knew of this year in our area to have been born so. She also said it was neurological and there probably were other hidden pathologies going on.
Thank you all for any illuminations you might be able to shed on this very disturbing event.