THE TROUBLE WITH EQUINE TITERS
When discussing vaccination options with horse owners, I am often asked, “Why can’t we just pull a titer?” When talking about immunization, “titer” refers to the amount of antibodies to a particular disease that can be found in the blood. In theory, a body with a high titer against a disease is properly prepared to fight it and an annual booster isn’t necessary. In people this may be true, but in horses it is not. In other words, even a horse with a “high titer” against the pathogens that cause a particular disease may not
actually be equipped to fight them off.
We can pull blood from a horse and get antibody numbers for nearly any disease but, with one exception, we don’t know what the numbers actually mean. Streptococcus equi, the bacterium that causes strangles, is the only titer for which we have reliable, interpretable science. You could, technically, pull a titer each year for strangles to make vaccination decisions, and some veterinarians do: The data needed to interpret
the results is available in the American College of Veterinary Internal Medicine’s consensus statement on S. equi. That said, there are other considerations to weigh regarding the strangles vaccine, such as efficacy and risks of side effects, so the titer is just one factor to consider.
For any other disease, however, it’s irresponsible to base vaccination decisions on titers. We simply do not have the scientific data needed to correctly interpret the results. --- Melinda Freckleton, DVM