355 Determining the bioavailability of copper carbonate (Emerald-C) and tribasic copper chloride relative to copper sulfate in feedlot steers under moderate antagonistic pressure

Abstract Copper (Cu) from Cu sulfate (CuSO4) may be more susceptible to antagonism when fed in cattle diets high in sulfur and molybdenum, but other Cu supplements may be better able to avoid this. The objective of this study was to determine the bioavailability of Cu carbonate (CuCO3; Emerald-C, Old Bridge Minerals, Old Bridge, NJ) and tribasic Cu chloride (TBCC; Intellibond-C, Selko, Indianapolis, IN) relative to CuSO4 when fed to steers supplemented with 2 mg Mo/kg DM and 0.1% S. Angus crossbred steers [n = 84; body weight (BW) = 282 ± 19.3 kg] were enrolled (n = 12 per treatment) in a 96-d study and fed a corn-silage based diet with one of seven Cu supplementation strategies: no supplemental Cu (CON), 5 or 10 mg supplemental Cu/kg DM from CuSO4, 5 or 10 mg supplemental Cu/kg DM from TBCC, or 5 or 10 mg supplemental Cu/kg DM from CuCO3. Steers were housed in pens equipped with GrowSafe feed bunks (GrowSafe Systems Ltd., Airdire, AB, Canada) with six steers per pen. The GLM procedure of SAS 9.4 was used to determine the bioavailability of CuCO3 and TBCC relative to CuSO4 using both liver and plasma Cu. The MIXED procedure of SAS was used to analyze liver Cu, plasma Cu, and growth performance data. Contrasts compared CON vs. 5 mg/kg, CON vs. 10 mg/kg, 5 mg/kg vs. 10 mg/kg, CuCO3 vs. CuSO4, TBCC vs. CuSO4, and CuCO3 vs. TBCC. The bioavailability of CuCO3 relative to CuSO4 based on liver and plasma Cu was 89 (P < 0.01) and 133% (P = 0.21), respectively. The bioavailability of TBCC relative to CuSO4 based on liver and plasma Cu was 88 (P < 0.01) and 100% (P = 0.82), respectively. Over the 96-d trial, liver Cu decreased 66% in CON, from 74 to 21 mg Cu/kg DM. Steers receiving CuCO3 had greater plasma Cu concentrations than those receiving TBCC on d 56 (P = 0.05) but were similar by d 96 (P = 0.39). Copper supplemented steers had greater dry matter intake (DMI) than CON (P = 0.01). Steers supplemented with CuCO3 had greater DMI than those receiving TBCC (P = 0.05). Steers receiving TBCC tended to have greater gain:feed than those receiving CuSO4 (P = 0.08), but gain:feed did not differ between CON and supplemented treatments (P ≥ 0.6). In conclusion, CuCO3 and TBCC may be less available to steers under moderate antagonistic pressure based on liver Cu, but Emerald-C CuCO3 may result in greater Cu in circulation. More research is needed to evaluate the impact of feeding CuCO3 on systemic Cu metabolism and how factors such as initial Cu status impact relative bioavailability results.