Selenium and Immune Response in Vaccinated Horses

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We’ve all heard that selenium can have an effect on the immune function of horses. A recent article in the Journal of Animal Science reported on a study from the University of Kentucky College of Agriculture and the Alltech Inc. Center for Animal Nutrigenomics and Applied Animal Nutrition that looked at the effect of selenium supplementation on vaccination response and immune function in mature horses.

Twenty-eight horses were grouped by age and sex and were randomly allocated to one of four dietary treatment groups: low selenium (LS), adequate selenium (AS), selenium and yeast (SP), and sodium selenite (SS). For 35 weeks, horses allocated to LS, SP, and SS received a low-selenium diet (0.06 mg/kg DM) with the intention to lower selenium stores. The AS group received an adequate selenium diet (0.12 mg/kg DM).

At week 22 and 25 of the repletion phase (when horses were finished with the depletion of the selenium phase and were placed on the diets in the study), horses were vaccinated intramuscularly with 10 mg ovalbumin (OVA). (Ovalbumin is albumin derived from egg whites; albumin is often used as part of the adjuvant in equine vaccines. An adjuvant is a substance that enhances the body's immune response to an antigen, such as a virus in a vaccine.)

“Horses were also vaccinated against equine influenza at week 25. Blood samples were collected for 7 weeks after initial vaccination for serum separation and at 0, 3, and 5 weeks post-vaccination for peripheral blood mononuclear cell (PBMC) isolation and whole blood cytokine mRNA evaluation,” reported the study. “The Se status of the horses was monitored using whole blood Se and glutathione peroxidase (GSH-Px) activity as indicators.”

At week 22, both selenium and GSH-Px were greater for the SP and SS groups compared with the AS and LS groups. The researchers noted that serum vitamin E was similar between groups.

The research showed that while some parameters of immunity and reaction to the influenza vaccination were not changed by selenium status of the horses (low, adequate, plus yeast, or high selenium), other measures of immune function in the study indicated that low selenium status in a horse could adversely affect cell-mediated immunity.

In other words, having the proper levels of selenium--which is known to assist the horse's proper immune function--is important to ensure the horse's immune system reacts appropriately to vaccination.