Date on Honors Thesis



Equine Science

Examining Committee Member

Dr. Shea Porr, PhD, Advisor

Examining Committee Member

Keely Doctorman, Committee Member

Examining Committee Member

Megan Taylor, Committee Member


The most common best management practice used to combat diseases in horses is vaccination, which can decrease the incidence or severity of illness. However, the duration of immunity will vary for each vaccination and must be considered for revaccination purposes. Titer concentration, which evaluates antibodies in the blood, may be a helpful way of determining how long an animal has immunity to a disease. Leptospirosis, a zoonotic, bacterial disease, can result in uveitis, potentially leading to blindness, and abortion in mares. One serovar, Leptospirosis pomona (L. pomona), is associated with most cases of clinical disease in horses in North America. There is one approved vaccine, specific for L. pomona, currently available for this disease. The objective of this study was to evaluate the immune response in horses to the L. pomona vaccine.

Forty previously unvaccinated horses from the Murray State University Equine Center were used in this study. None had previously documented issues with uveitis or abortion. Blood was drawn and serum removed for evaluation of leptospirosis titers. Horses were then divided into TRT (vaccinated, n=20) or CON (not vaccinated, n=20), and TRT horses were vaccinated for leptospirosis. Blood samples were collected from 37 (TRT n=20; CON n=17) horses 14 d post-vaccination. Horses in the TRT group received booster vaccines 3 weeks after the first vaccination. Blood samples were again collected from 37 horses 14 d post booster. At each collection, 20 ml of blood were collected by jugular venipuncture into 2 red top vacutainers® tubes. Samples were centrifuged and serum removed within 24 hours. Serum was delivered to the Breathitt Veterinary Center and either analyzed within 48 hours or frozen until analysis could be completed. Descriptive statistics were used to evaluate the results.

Preliminary results showed a higher seroprevalence of L. pomona in this study (8%, n=3 of 37) when compared to previously published research of unvaccinated horses. Kitson-Piggot and Prescott (1987) found that only 4% of horses in Ontario had a positive titer for L. pomona, and Fagre et al. (2020) found only a 1% incidence for the same serovar in horses in Colorado. Given that the location for horses in the previous studies were spread out over a larger geographical distance than the horses in this study, it is possible that the University horses were concentrated and exposed to a greater degree than horses in the other studies. After the initial vaccination was administered, all horses in the TRT group showed an increase in antibody concentration which resulted in a positive titer for each horse. Titers increased at varying rates, ranging from 1:200 to 1:25600. After receiving the booster vaccination, five TRT horses showed no change in titer, six horses had another increase, and nine horses showed a decrease in titer concentration. No horses showed any signs of illness related to leptospirosis during the study. Further analysis of the results may lead to greater understanding of the equine immune response to this vaccine.