The next AMA is March 14th. I am not sure I have the answer to which Mg is more bioavailable. I will need to look at this. The research on PSSM is evolving and seems to be gaining traction as a popular subject though the number of horses affected by this overtly may be few relative to other diseases such as colic, laminitis, EMS, etc. But I will try to find something on this in the limited material that I would trust on this subject. There is SO MUCH we need to learn….. overwhelming!