Bioavailability of copper from tribasic copper chloride and copper sulfate in growing cattle

Two experiments were conducted to determine the bioavailability of copper (Cu) from tribasic Cu chloride (Cu2(OH)3Cl) relative to Cu sulfate in growing steers. Experiment 1 compared tribasic Cu chloride to sulfate in terms of ability to maintain Cu status when supplemented to steers fed diets high in the Cu antagonists, molybdenum (Mo) and sulfur (S). Sixty Angus and Angus × Hereford steers (257 ± 2 kg body weight) were stratified by body weight and randomly assigned to treatments. Treatments consisted of 0, 5 or 10 mg supplemental Cu/kg diet DM from either Cu chloride or Cu sulfate. All diets were supplemented with 5 mg Mo/kg and 1.5 g S/kg. The control corn silage based diet analyzed 4.9 mg Cu/kg and 6.9 mg Mo/kg and was calculated to contain 3.0 g S/kg. Plasma and liver Cu concentrations and plasma ceruloplasmin activity decreased (P < 0.01) in all treatment groups during the 98-day study. Copper supplemented steers had higher (P < 0.01) plasma Cu, plasma ceruloplasmin, and liver Cu than controls at the end of the study. Steers supplemented with 10 mg Cu/kg had higher (P < 0.01) plasma Cu, plasma ceruloplasmin, and liver Cu than those receiving 5 mg Cu/kg diet. Bioavailability of Cu from Cu chloride, relative to Cu sulfate, was estimated from plasma Cu and ceruloplasmin on day 84 and liver Cu on day 98 using multiple linear regression and a slope ratio technique. Compared with Cu sulfate (1.00), relative bioavailability of Cu from tribasic Cu chloride was 1.32 (P < 0.08), 1.18 (P < 0.38) and 1.96 (P < 0.04) based on plasma Cu, plasma ceruloplasmin and liver Cu, respectively. In experiment 2, 43 Angus and Simmental steers (375 ± 7 kg BW) that had previously been depleted of Cu were used in a 21-day repletion study. Steers were randomly assigned within breed to treatment, and individually fed a corn silage based diet low in Mo (1.18 mg/kg). Treatments consisted of 0, 50 or 100 mg supplemental Cu/day from either Cu chloride or Cu sulfate. Plasma Cu, plasma ceruloplasmin and liver Cu increased (P < 0.01) in Cu supplemented, but not in control, steers. Plasma and liver Cu concentrations increased (P < 0.01) to a greater extent in steers receiving 100 mg Cu/day compared to those given 50 mg Cu/day. Tribasic Cu chloride and Cu sulfate were similar (P > 0.10) in their ability to increase Cu status in Cu depleted steers fed a diet low in Mo. Tribasic Cu chloride is more bioavailable than CuSO4 when added to diets high in the Cu antagonists Mo and S. When evaluated in Cu depleted steers fed diets low in Mo, the two Cu sources had a similar bioavailability.