s / Journal of Equine Veterinary Science 33 (2013) 321-399 338 (P 1⁄4 0.004) and TrxR1 (P 1⁄4 0.04) expression were affected by time, with a reduction in mRNA abundance of both selenoproteins at 24 h post-exercise (P< 0.05) compared to pre-exercise. A trend for a time*treatment affect was also observed for PBMC GPx1 (P 1⁄4 0.08) and TrxR1 (P 1⁄4 0.06). Expression of GPx1 was reduced at 24 h post-exercise (P 1⁄4 0.001) and TrxR1 increased at 6 h post-exercise (P 1⁄4 0.04) compared to pre-exercise values in HIGH-Se horses, but expression of both selenoproteins remained unchanged following exercise in NRC-Se. As a result, mRNA abundance of GPx1 (P 1⁄4 0.038) and TrxR1 (P 1⁄4 0.012) was greater in HIGH-Se than NRC-Se horses at 6 h post-exercise. Feeding Se at 3X the current NRC recommendation increased selenoprotein gene expression following prolonged exercise, which could indicate greater antioxidant support during exercise recovery. However, no change in cytokine mRNA expression indicates that a higher level of dietary Se may not attenuate exerciseinduced immunosuppression.