I would call the vet and get the information directly from him.
Moldy corn wouldn't affect the sacrum, so it may not be what the trainer was talking about. But then again, I have never heard of "corn cob disease" nor can I think of any disease related to corn that would affect the sacrum.
Studies show that we only remember accurately about 1/2 of what our vet says ;)
Licensed Veterinary Technician