Eight stallions have so far tested positive for CEM and agricultural authorites in about 40 states are tracing 334 horses potentially exposed to the venereal disease.
Revised import requirements announced by the Canadian Food Inspection Agency (CFIA) cover all live horses, semen and embryos entering Canada from the US.
No import permits are required for live horses provided the animals have not been on properties where the bacteria responsible for CEM has been detected during the previous 60 days or on premises currently under quarantine or investigation for CEM.
Any mares must not have been bred naturally to, or inseminated with, semen from a stallion positive for CEM, or a stallion living on a property where positive tests have been returned, or under quarantine or investigation for CEM.
Permits are still required for some horses from Florida, due to that state's outbreak of equine piroplasmosis.
Semen collected after December 15 last year will now require an import permit along with certification that the onor stallion has not been on a premises quarantined or positive for CEM in the preceding 60 days.
Requirements for embryos are similar.