RECOVERY RATE AND PLASMA ZINC AND COPPER CONCENTRATIONS OF STEER CALVES FED ORGANIC AND INORGANIC ZINC AND MANGANESE SOURCES WITH OR WITHOUT INJECTABLE COPPER AND CHALLENGED WITH INFECTIOUS BOVINE-RHINOTRACHEITIS VIRUS

Two experiments were conducted using feeder calves in a randomized block design to determine the effects of organic and inorganic sources of Zn and Mn fed pre- and posttransit (Exp. 1 and 2) with or without injectable Cu(Exp. 2) on DMI, rectal temperature, BW changes, and plasma Zn and Cu concentrations of feedlot steers challenged with infectious bovine rhinotracheitis virus (IBRV). In Exp. 1, before weaning, all steers and their dams received the following free-choice mineral supplements: 1) control (no supplemental Zn or Mn), 2) ZnO + MnO (ZnMnO), and 3) Zn methionine + Mn methionine (ZnMnMet). In Exp. 2, 18 d before weaning and shipping, steers were allotted into two groups (22 steers/group) and fed 225 mg of Zn-steer(-1) d(-1) in .9 Bg of ground corn as ZnO or ZnMet. Half of the steers from each group were injected (s.c.) with 120 mg of Cu from Cu glycinate. Steers (Exp. 1 and 2) were weaned and shipped approximately 2,500 inn to the feedlot, where they received the same supplements in the form of a complete diet for 34 d, during which time calves recovered from the stress due to shipment. All steers were initially sere-negative to IBRV. On d 34 (d 0 of IBRV), all steers were challenged with IBRV and DMI, rectal temperature, and BW change were monitored for 28 d. In Exp. 1, steers fed ZnMnMet tended (P < .10) to average 11 kg of BW higher than the control steers. Seven days after IBRV challenge, the steers fed control, ZnMnO, and ZnMnMet had 48, 25, and 18% decreases (P < .05) in plasma Zn concentration compared to pretrial values, respectively. In Exp. 2, there were no Zn source x Cu interactions. Steers injected with Cu had 30 and 6.9% lower (P < .05) DMI and BW change, respectively, than steers not injected with Cu. These data indicate that ZnMnMet sustained BW change and plasma Zn concentrations of IBRV-stressed steers (Exp. 1). Contrarily, Cu injection or abscesses resulting from it decreased DMI and BW change of LBRV-stressed steers (Exp. 2).