ABSTRACT
Beef heifers which had grazed 'Jose' tall wheatgrass (TWG; Thinopyrum ponticum var. 'Jose'; 10 heifers) and creeping wildrye (CWR; Leymus triticoides var. 'Rio'; 10 heifers) with high levels of Se (>2 mg/kg DM) due to growth in saline soils, accumulated high Se levels in blood, liver and muscle (Juchem et al., 2012). We determined the decrease in Se levels in blood, liver and muscle from these heifers, particularly the decrease of Se in muscle, in order to determine the maximum feeding length of a low Se diet (LSeD) required sustaining Se-enriched beef. Immediately after grazing, all heifers were fed a LSeD containing <0.30 mg/kg DM for 209 d. Blood, liver and muscle samples, as well as body weight (BW), were collected at the beginning and end of the LSeD feeding period and at intermediate times. After grazing, CWR and TWG heifers had similar BW, but TWG heifers had higher levels of Se in whole blood (1.19 versus 0.81 mg/L), liver (2.67 versus 2.12 mg/kg wet weight (WW)), and muscle tissue (0.87 versus 0.63 mg/kg WW) than CWR heifers. The Se levels decreased with exposure time to the LSeD and, at 82 d of feeding the LSeD, Se levels were 77 (liver), 49 (blood) and 31% (muscle) lower. The BW gains for both groups were ~0.5 kg/d during the first 82 d of feeding, but increased thereafter. Levels of Cu in serum (0.28 versus 0.50 mg/L) and liver (1.14 versus 22.9 mg/kg WW) were lower at the end of grazing in TWG heifers, and suggested a potential Cu deficiency. Grazing forages with high Se levels can result in Se-enriched beef, but a LSeD feeding period of <82 d is required to maintain enrichment.
