Metabolic Horses and Immunity: Response to Vaccination

Equine metabolic syndrome (EMS), often associated with abnormal fat deposits, insulin dysregulation, and a history of chronic laminitis, continues to affect horses, many of which are overweight. In addition to the perils of obesity and abnormal insulin responses, one recent study* shows that EMS may also take its toll on a horse’s immune system.

“Research in other mammals shows that overweight animals, including mice and humans, have an impaired immune response to vaccination,” relayed Laura Petroski, B.V.M.S., a veterinarian for Kentucky Equine Research.

For example, one study involving the human influenza vaccination identified a positive correlation between body mass index and higher initial antibody responses, meaning overweight humans produced more antibodies against the flu virus. One year after vaccination, however, higher body mass index was correlated with a greater decline in influenza antibody titers.

To explore whether similar obesity-related immunity alterations occur in overweight horses with EMS, researchers recruited EMS horses and healthy controls, and vaccinated them against equine influenza. Vaccination response was followed for five weeks.

Compared to control horses, all vaccinated horses responded with significant increases in vaccine titers, as well as antibodies specific to the equine influenza virus (IgGa and IgGb). There was no difference in these values between horses with and without EMS.

“Metabolic status did, however, influence other aspects of the horses’ immune systems. Specifically, EMS horses had a lower gene expression of two signaling molecules that play important roles in the immune system,” shared Petroski.

She added, “These findings suggest that horses with EMS appear to have a reduced response to vaccination compared to metabolically normal, or non-EMS, control horses.”

Additional research is warranted, specifically to determine vaccine efficacy and duration of immunity in obese and EMS horses.

“Other ways of ensuring your horse receives all the benefits of vaccination include offering a well-balanced diet and an omega-3 fatty acid supplement, such as EO-3 from Kentucky Equine Research,” Petroski advised. “Studies show that supplementation with omega-3 fatty acids improves responses to vaccination in horses.”

*Elzinga, S., S. Reedy, V.D. Barker, et al. 2018. Humoral and cell-mediated immune responses to influenza vaccination in equine metabolic syndrome (EMS) horses. Veterinary Immunology and Immunopathology 199:32-38.