Call a vet ASAP!!!! If a vet can't/won't come out, throw the baby into the cab of your truck and take it there!
Are you SURE it hasn't gotten up at all? Have you been watching it constantly? Babies do lay down and sleep a lot. If you're sure it hasn't fed, it is probably greatly dehydrated. Also, it is missing out on the colostrum. Try milking the mare and giving the baby a bottle or syringe it in. This is an emergency and something needs to be done NOW!!!! Good luck and keep us posted.