Response of Timothy Se Concentration to Increasing Rates of a Slow-Release Se Fertilizer in Eastern Canada.

Selenium is an essential micronutrient given to ruminants by injection or orally, or applied as an additive to fertilizers to raise crop Se concentration in areas with low-Se soils. We determined the response of timothy (Phleum pratense L.) Se concentration to increasing rates (0, 5, 10, 15, 20, and 25 g of Se ha^-1) of a slow-release Se fertilizer (Selcote Ultra®, SU) applied in spring of 2010 at three sites in Québec (Canada) and investigated the possibility of predicting forage Se concentration by near infrared reflectance spectroscopy (NIRS). The response of timothy Se concentration (y, mg kg^-1 dry matter, DM) to increasing Se rates (x) was similar at the three sites; averaged across sites, it increased linearly with increasing Se rates at the first (y = 0.012 + 0.0292 x; R² = 0.98) and second harvest (y = 0.052 + 0.0091 x; R² = 0.96) in the year of spring Se application, and in the first harvest of the subsequent year (y = 0.012 + 0.0117 x; R² = 0.97). Selenium fertilization did not affect timothy DM yield, fiber concentration, and digestibility. Timothy Se concentration could not be successfully predicted by NIRS. A spring application of 10 g Se ha^-1 as a slow-release fertilizer and its residual effect are sufficient to produce timothy with adequate Se concentration (> 0.1 mg kg^-1 DM) to prevent deficiency diseases in livestock and allow diet formulation to meet optimal Se levels.