Selenium Incorporation and Performance of Beef Cattle Grazing Pastures Irrigated with Saline-Sodic Drainage Water.

Selenium incorporation and animal performance were investigated in beef cattle grazing perennial forage pastures previously irrigated for 4-7 years with saline drainage water at Red Rock Ranch, westside San Joaquin Valley of California.  During the 2007-2008 study period mainly tailwater was applied to the pastures due to a shortage of drainage water, but soil salinity remained high (>14 dS/m ECe) as did total Se in soil (2-3 ppm).  Each year, 20 Galvi Black Angus heifers from a single herd were divided into 4 groups with nearly equal total body weight.  Twenty acre pastures of tall wheatgrass (TWG), Thinopyrum ponticum var. ‘Jose’ and creeping wildrye (CWR), Leymus triticoides var. ‘Rio’ were divided into four equal paddocks, subdivided into north and south sections that were each rotationally grazed by a group of 5 heifers.  Forage dry matter (standing biomass) was sampled before and after the heifers entered a paddock.  Heifer body weights were taken, along with blood, liver and muscle samples.  In 2007, blood Se increased rapidly from 0.15 ppm to over 0.5 ppm (upper limit of “normal range”) within 50 days of grazing the pastures.  Heifers grazing TWG forage had blood Se concentrations similar to those grazing CWR forage (0.9 ppm) after 195 days of grazing.  In 2008, blood Se increased more rapidly in TWG heifers and was higher (1.2 ppm) than in CWR heifers (0.8 ppm) at the end of grazing. In both years, Se concentrations in the liver after grazing were 4 to 8 times higher than recommended maximums (i.e., 0.5 ppm).  Acceptable body weight gains and absence of clinical signs of Se toxicity suggest that young beef cattle can safely graze these high Se forages for one season.