An outbreak of Equine viral arteritis (EVA) occurred on a Quarter Horse breeding farm in New Mexico in June of this year and the ensuing dissemination of infection to farms both within and outside the state raises significant issues and conclusions. These issues include the management and veterinary procedures employed by the Quarter Horse industry to maximize reproductive performance by extensive use of artificial insemination and embryo transfer, which contributed to the spread of EVA.

When an infectious disease outbreak occurs, it is imperative that a prompt and accurate diagnosis is obtained. Preventive measures can then be immediately implemented to restrict the spread of infection and mitigate serious disease and economic losses. Accepting that EVA has now become established within the Quarter Horse population, it will be necessary to introduce a preventive program of vaccination accompanied by appropriate monitoring to determine the extent of this infection within the population.

In early June, the farm owner, a veterinarian, became concerned that mares previously identified as pregnant were, upon re-examination, found to be “empty.” By June 16, the increasing number of losses prompted the owner to seek advice as to the possible cause. Sera and semen samples were submitted to the Maxwell H. Gluck Equine Research Center at the University of Kentucky. The Gluck Center made the recommendation, which was accepted, that shipment of semen from stallions on the farm be halted. On June 23, results revealed very high antibody titers to equine arteritis virus in the majority of the sera, and by June 26, the virus had been isolated from the semen of two stallions. These findings provided very strong circumstantial evidence of recent exposure to the virus, which was later confirmed by examination of paired sera from individual animals.