The ongoing investigation into contagious equine metritis (CEM) now includes more than 700 exposed or positive horses, according to the USDA.  

The investigation began in mid-December 2008, when a Quarter Horse stallion on a Kentucky farm tested positive during routine testing for international semen shipment.

According to the USDA’s Animal and Plant Health Inspection Service (APHIS), as of March 24 the positive horses included 13 stallions and three mares. In addition to these horses, they had confirmed the locations of 695 horses exposed to Taylorella equigenitalis. The 711 horses were located in 46 states. There were 112 exposed or positive stallions in 19 states and 599 exposed or positive mares in 44 states. Authorities were still actively tracking six exposed mares and four exposed stallions.

An exposed horse is one that was bred to a positive horse, either naturally or via artificial insemination, or one that is otherwise epidemiologically linked to a positive horse, as determined by animal health officials