"Infectious disease is common in horses; for this reason we use vaccination as an important component of our preventive strategy. Nevertheless, we're often left with a lack of studies and information that could be important (in decision-making regarding vaccination)," said Paul Lunn, BVSc, MS, PhD, head of the Department of Clinical Sciences at Colorado State University's College of Veterinary Medicine. He and other veterinarians saw that need for research, and at the 2003 American Association of Equine Practitioners' convention, Lunn presented studies that he and six other scientists completed comparing immune responses between commonly used, commercially available vaccines.

The scientists performed two studies. First, they did a seroconversion study of equine influenza virus (EIV), equine herpesvirus-type 1 (EHV-1), and Eastern equine encephalitis (EEE), vaccines. Second, they did a study looking at the immune responses to two EHV-1 anti-abortion vaccines.

The horses used in both studies consisted of aged, non-pregnant mares whose full vaccination histories were not available, although it was thought that the majority would have received annual spring vaccinations in the past. The mares were all maintained in a single barn in one large group and were run through a chute system for sample collection and vaccination. Each had an electronic chip implanted for identification