An evaluation of the role of organic selenium in immune function in cattle.
Covey, Tanya L.
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Selenium (Se) plays a vital antioxidant role as a constituent of glutathione peroxidase (GSH-Px). Newly received feedlot cattle are exposed to multiple factors that can lead to oxidative stress, including viral infection. The objective of the research conducted for this dissertation was to evaluate the effects of different Se sources on immune function (Exp. 1) of calves challenged with infectious bovine rhinotracheitis virus (IBRV) and on health and performance in a field study (Exp. 2). In Exp. 1, 24 Holstein steers (BW = 148.2 ± 2.79 kg) were assigned randomly to treatments, including: 1) Control = no supplemental Se; 2) Sel-Plex = 1 mg/(steer•d) of Se from Se yeast (Sel-Plex; Alltech Inc., Nicholasville, KY); or 3) Selenite = 5 mg/(steer•d) of Se from sodium selenite. The Se sources were fed for 28 d before steers were intranasally inoculated with IBRV (d 0) and continued through 21 d after the challenge. Treatments did not affect body weight (P > 0.05) or feed intake (P > 0.30) before or after the challenge. Whole blood Se concentrations were greater (P < 0.01) when Sel-Plex was fed than with the other two groups, but GSH-Px activity (P > 0.20) was not affected by treatment. Supplemental Se tended (P = 0.08) to increase IBRV titer values on d -14 but to decrease (P = 0.06) titers on d 21. Steers fed Sel-Plex tended (P = 0.08) to have lower rectal temperatures for 18 h before the challenge than steers fed selenite, but there were no other differences (P > 0.10) in rectal temperature. Serum interleukin-1b concentrations were lower overall (P = 0.02) and tumor necrosis factor-á concentrations 12 h after the challenge were greater (P = 0.04) in steers fed Sel-Plex than in those fed Selenite. In Exp. 2, crossbred newly received heifers (4 pens/treatment) were fed the same treatments as in Exp. 1, except that Selenite supplied 1 mg/(heifer•d). No differences (P > 0.10) among treatments were noted for performance or health during the 28-d study. Additional research is needed to clarify how providing Se in the form of Sel-Plex affects immune response to viral infections in cattle.