Effects of Selenium Source on Mares and Foals

The micromineral selenium plays a vital role in equine immune function, especially in the mare and foal. Selenium transfer through the placenta and milk has been shown to influence neonatal selenium status in livestock, but it remains unknown if the selenium source affected transmission from mare to foal.

To that end, a research team--led by Julia B. Montgomery, MedVet, PhD, Dipl. ACVIM, from the Department of Veterinary Biomedical Sciences at the Western College of Veterinary Medicine--recently carried out a study examining the effects of organic or inorganic formulations of the mineral on mares' and foals' selenium levels. In addition they measured several immune function parameters in the foal.

Montgomery and colleagues fed 20 pregnant Standardbred mares identical balanced diets (which included selenium-deficient forage) starting two months prior to foaling and continuing to one month post-foaling. The team randomly assigned the mares to consume 0.3 ppm of either organic or inorganic selenium in addition to their regular rations.

The team collected colostrum and milk from each mare and blood samples from mares and foals to determine the animals' selenium status.

Upon reviewing their results, the team found that:

  • The selenium source did not affect the mares' blood, colostrums, or milk selenium levels; however, both groups' concentrations were below the range considered adequate for mature horses; and
  • Foals born to mares receiving the organic formulation had blood selenium concentrations 170% higher at one month of age than foals from mares receiving the inorganic supplement.

Although there were no differences in the mares' colostrum or milk selenium levels, the increased levels in foals of mares consuming the organic supplement suggest that there is greater transplacental transfer of organic selenium during late gestation than inorganic selenium.

Additionally, in terms of immune function there was no difference in IgG (immunoglobulin G, or the foal's antibodies) concentration in either group of foals. However, foals from mares consuming organic selenium showed a significant increase in the relative gene expression of three important immune parameters: interleukin-2, tumor necrosis factor-alpha, and interferon gamma.

This means that foals from mares fed organic selenium could be capable of producing more lymphocytes (a type of white blood cell that plays a central role in directing and coordinating immune responses) than other foals and, thus, have an enhanced cellular immune response.

It’s important for all horses—including pregnant mares—to consume a diet containing adequate selenium, which the National Research Council defines as 0.1 mg/kg dry matter diet.

The article, "The Effects of Selenium Source on Measures of Selenium Status of Mares and Selenium Status and Immune Function of Their Foals," appeared in June 2012 in the Journal of Equine Veterinary Science. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.