The International Collating Center, Newmarket, and other sources reported the following disease outbreaks:

A case of contagious equine metritis in a Thoroughbred mare was reported from Japan. Respiratory disease attributable to equine herpes virus (EHV) was reported extensively from France among several breeds of horses. In the United Kingdom, respiratory disease attributable to EHV was diagnosed on several equine premises, and EHV-1 was isolated at postmortem from a zebra, which died following respiratory distress.

Abortion caused by EHV-1 was reported from France in trotting and saddle mares; from Germany, in four Thoroughbred mares on four premises; from Ireland, in five mares on five premises; from Japan, in 11 mares on seven premises; and from Switzerland, three cases. The United Kingdom reported cases on six premises. On one farm there were 11 abortions among unvaccinated non-Thoroughbred mares. In three cases on other premises, EHV-1 was diagnosed by positive PCR of the placentae but not of the fetuses of vaccinated mares. EHV-1 was also diagnosed in a foal that died from a mare diagnosed with EHV-1 abortion the previous year. In Central Kentucky between August 2003 and the end of March 2004 there were 25 cases among Thoroughbred and five cases among non-Thoroughbred mares on 26 premises. The paralytic form of EHV-1 was reported on two premises in the United Kingdom.

Equine influenza was diagnosed at the San Isidro Training Center in Argentina; among several breeds at many different premises in France; at a trotting racetrack in Rome, Italy; on two premises in Ireland; among ponies on two premises in Sweden; and on three premises in the United Kingdom