The effect of dietary selenium on humoral immunocompetence of ponies

Fifteen Shetland ponies were used in a 7-wk trial to study the effect of supplemental Se on humoral antibody production. Four 3-yr-old, five 2-yr-old and six yearling ponies were depleted of Se before being assigned randomly to either a low Se (.02 ppm) or higher Se (.22 ppm) diet. Each pony was challenged antigenically with 2 ml of sheep packed red blood cells upon receiving its respective diet and again 2 wk post-treatment. Blood samples were drawn weekly and assayed for glutathione peroxidase activity, Se and immunoglobulin concentration and antibody titers. Compared with those ponies receiving the low Se concentrate, ponies receiving the Se-supplemented diet had higher (P less than .01) glutathione peroxidase activities and blood Se concentrations during the later weeks of the experiment. An enhanced primary response was observed in Se-supplemented ponies as evidenced by increased hemagglutination titers. Higher IgG concentrations (P less than .01) also were observed in the Se-supplemented group. Dietary Se concentration of .02 ppm was inadequate for optimum immune function in the equine.