Understanding Potomac Horse Fever Potomac horse fever (PHF), or equine monocytic ehrlichiosis as it is currently termed, still occurs in areas of the United States. It can often pose a diagnostic challenge because of its varied clinical presentations. Read More Ask The Vet Early Pregnancy Loss Q. While my 21-year-old broodmare was being treated for a guttural pouch infection last year, she was successfully bred. Two months later she lost the embryo. Could the guttural pouch infection be the reason? A. Read the vet's answer