Effects of Trace Mineral Supplementation, Source, and Growth Implants on Immune Response of Growing and Finishing Feedlot Steers

Abstract

<h2>ABSTRACT</h2> To determine the effects of growth implants and trace mineral (TM) supplementation and source on immune response, 375 steers (approximately 7 mo of age and 250.0 ± 11.0 kg), stratified by initial body weight, were randomly assigned to 1 of 36 pens that were then randomly assigned to treatments. Treatments consisted of 1) control (no supplemental Cu, Zn, Mn, and Co), 2) inorganic TM (CuSO₄, ZnSO₄, MnSO₄, and CoCO₃), and 3) organic TM (iso-amounts of organic Cu, Zn, Mn, and Co). On d 28 post-arrival to the feedlot, steers from 6 pens per treatment received a growth implant containing 200mg progesterone and 20mg estradiol benzoate, whereas the other half of the steers within the same treatment (6 pens) did not receive a growth implant. Steers were fed a corn silage-based growing diet for 56 d and were then gradually switched toa high-concentrate finishing diet. At the beginning of the finishing phase, only steers receiving growth implants during the growing phase were reimplanted with 80mg of trenbolone acetate and 16mg of estradiol. During the finishing phase, all minerals excluding Zn were fed at NRC recommended concentrations in inorganic form. Treatments during the finishing phase consisted of 1) control (no supplemental Zn), 2) inorganic Zn (30mg Zn/kg DM from ZnSO₄), and 3) organic Zn (iso-amounts of organic Zn). At the end of the growing phase, steers receiving organic TM had greater (P < 0.02) total IgM concentrations than inorganic-supplemented steers, and implanted steers tended (P < 0.07) to have greater IgG antibody titer concentrations specific for pig red blood cells than nonimplanted steers. During the finishing phase, steers supplemented with organic Zn had greater (P = 0.04) ovalbumin antibody titer concentrations than steers supplemented with inorganic TM.Superoxide dismutase activity, interferon gamma concentrations, and antibody titers specific to pig red blood cells and infectious bovine rhinotracheitis virus were unaffectedby TM treatment or growth implants.