Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 3, 2003
Publication Date: June 3, 2003
Citation: WSASAS Proc. 53:534-36, 2003. Interpretive Summary: Diets containing feeds (e.g., grains, hays) naturally high in selenium appear to initially (first 7 days) induce higher concentrations of selenium in the plasma of steers at a more rapid rate when compared to diets formulated with inorganic selenium salts. However, after consuming the high selenium diets for 21 days, steers in this study had similar levels of plasma selenium regardless the form of selenium consumed. Additionally, these plasma levels were higher at day 21 when compared to plasma selenium levels before the beginning of the study. It has been suggested that the majority of Se in wheat exists as selenomethionine. Furthermore, since 60 to 70% of selenium in pasture grasses has been reported to be associated with the protein fraction, some suggest that a large portion of forage Se is also selenomethionine. Therefore, the molecular form of selenium that exists in the high selenium feeds used in this study may be the reason for the plasma response observed during the first 7 days.
Technical Abstract: Selenium (Se) status and deposition in edible muscle of beef cattle are greatly influenced by dietary Se. However, limited data are available describing these events in finishing steers consuming feeds naturally high in Se. Therefore, in order to assess the effects of high Se feeds (natural and artificial) on Se status, 45 cross bred steers (BW = 351.1 ± 24.1 kg) were stratified by BW and randomly assigned to one of four dietary treatments: Se adequate (CON; n = 12), or Se provided as high Se wheat (WHT; n = 11), high Se hay (HAY; n = 11), or selenate supplement (SEO; n = 11). Selenium content for WHT, HAY, and SEO diets was 60 to 70 ug·kg-1 BW·d-1, and for CON, 7 to 12 ug·kg-1 BW·d-1. Diets were similar in feedstuff composition (25% wheat, 39% corn, 25% grass hay, 6% desugared molasses, and 5% wheat middling based supplement on a DM basis), isonitrogenous and isocaloric (14.0% CP, 2.12 Mcal NEm·kg-1, and 1.26 Mcal NEg·kg-1 DM), and offered once daily (1500), individually to steers in a Calan Gate system. Beginning with d 0, BW was measured and plasma samples collected every 7 d until d 21 and every 21 d thereafter. Plasma Se for the first 21 d were 76.0, 144.3, 141.7 and 124.9 ± 9.1 ng·mL-1 for CON, WHT, HAY, and SEO, respectively. All high Se treatments exhibited a quadratic (P < 0.03) increase in plasma Se from d 0 to 21; however, no changes (P > 0.38) were observed for CON. Plasma Se was not different (P > 0.63) between treatments on d 0 (79.2 ± 7.9 ng·mL-1), but on d 7, WHT and HAY, and on d 14 and 21, WHT, HAY, and SEO were greater (P < 0.03) than CON. Plasma Se in HAY was also higher (P < 0.02) than SEO on d 14. Steer ADG were not different (P > 0.33) between treatments for the first 21 d and was 1.55, 1.65, 1.55 and 1.52 ± 0.11 kg·d-1 for CON, WHT, HAY, and SEO, respectively. In conclusion, Se provided by WHT and HAY seemed to elevate plasma Se earlier (d 7 and 14) than SEO; however, by d 21, all high Se treatments were not different from each other and elevated over CON.