It appears that the research needed to definitively answer your question has not been done. In one scientific study, foals from infected mares did receive antibodies to EPM through ingestion of colostrum; however, none of the foals were reported to have contracted the clinical disease from their dams. In regard to the signs, treatment, etc., the American Association of Equine Practioners (AAEP) has an informational article on EPM at:
http://www.xcodesign.com/aaep/displayArticles.cfm?ID=248
If your brood mare has clinical signs of EPM, it is wise to consult your local veterinarian about treatment options available.
