Effects of copper source and concentration on copper status and immune function in growing and finishing steers

Forty-eight individually fed purebred Angus steers (7±1.1 mo of age, 218±9.1 kg BW) were used to determine the effects of copper (Cu) source and concentration on Cu status and immune function. Steers were stratified by weight and initial liver Cu concentration and randomly assigned to one of five treatments. Treatments were: (1) control (no supplemental Cu), (2) 10 mg Cu/kg dry matter (DM) from Cu sulfate (CuSO4), (3) 10 mg Cu/kg DM from a Cu-amino acid complex (Availa Cu; Zinpro Corporation, Eden Prairie, MN, USA), (4) 20 mg Cu/kg DM from CuSO4, and (5) 20 mg Cu/kg DM from Availa Cu. Steers were housed in individual pens and fed an alfalfa-corn based growing diet (7.1 mg Cu/kg DM) for 56 d then gradually switched to a high concentrate diet (6.1 mg Cu/kg DM) for 144 d. On d 56 of the growing phase and d 112 of the finishing phase, liver Cu concentrations were higher (P<0.01) in Cu supplemented steers. Steers receiving 20 mg Cu/kg DM had higher (P<0.01) liver Cu concentrations than steers receiving 10 mg Cu/kg DM. On d 112 of the finishing phase, steers receiving 20 mg Cu/kg DM from Availa Cu had higher (P<0.01) liver Cu concentrations than steers supplemented 20 mg Cu/kg DM from CuSO4. Cell mediated immune response to phytohemagglutinin was higher (P<0.01) in steers supplemented with 20 mg Cu/kg DM compared to steers supplemented with 10 mg Cu/kg DM. Total immunoglobulin (Ig) and immunoglobulin G (IgG) concentrations specific to pig red blood cells (PRBC) were higher (P<0.01) in steers supplemented with 10 mg Cu/kg DM from CuSO4 than steers supplemented with 10 mg Cu/kg DM from Availa Cu. During the finishing phase, IgG concentrations specific to PRBC were higher (P<0.03) and antibody titers specific to ovalbumin (OVA) were lower (P<0.05) in control steers relative to Cu supplemented steers. Steers receiving 20 mg Cu/kg DM had higher (P<0.02) antibody titers specific to OVA than steers receiving 10 mg Cu/kg DM. Steers receiving 20 mg Cu/kg DM from Availa Cu had higher (P<0.01) antibody titers specific to OVA than steers supplemented with 20 mg Cu/kg DM from CuSO4. Results indicate that the immune response to an antigen varies depending on the type of antigen administered as well as the concentration and source of Cu supplemented.