PSVIII-28 Influence of dietary copper concentration on rumen fermentation characteristics in beef steers.

Abstract Twelve crossbred steers (body weight; BW: 720 ± 12.3 kg; approximately 5 yr old) fitted with ruminal cannulas were utilized to examine the impact of dietary Cu concentrations on rumen fermentation characteristics. All animals were blocked by BW, housed in individual pens with automatic waterers, and randomly assigned, within block, to one of three treatments. Treatments consisted of: 0 (control), 10, or 20 mg supplemental Cu/kg DM from Cu sulfate (CuSO4∙5H2O). Steers were fed a steam-flaked-corn-based diet (DM basis: 4.8 mg of Cu/kg DM, 13.2% crude protein, and 1.53 Mcal/kg NEg). Diets were delivered daily in amounts to allow for ad libitum access to feed over a 24 h period. Dietary Cu treatments were supplemented for 28 d prior to rumen fluid collection 2 h post-feeding. Data were analyzed as a randomized block design using the MIXED procedure of SAS with individual animals as the experimental unit. Significance was defined as P ≤ 0.05. Ruminal pH was not affected (P = 0.85) by Cu supplementation. Ruminal soluble Cu concentrations were greater (P < 0.05) in steers receiving 20 mg Cu/kg DM when compared to the control and 10 mg Cu/kg DM treatments. Steers receiving 10 mg Cu/kg DM had greater (P < 0.05) rumen soluble Cu concentrations than control. Steers receiving 20 mg Cu/kg DM had lesser (P < 0.05) Cu²⁺ as a proportion of total soluble Cu concentrations compared to control and 10 mg Cu/kg DM treatments. Steers receiving 10 mg Cu/kg DM had lesser (P < 0.05) Cu²⁺ as a proportion of total soluble Cu concentrations than control. Redox potential was greater (P = 0.05) in steers receiving 20 mg/kg DM compared to the control and 10 mg Cu/kg DM treatments. Cu supplementation did not affect total VFA concentrations (mM; P = 0.67). Molar proportions of acetate (P < 0.47) and butyrate (P < 0.09) were similar across treatments. However, molar proportions of propionate were lesser (P = 0.05) in steers receiving 20 mg Cu/kg DM when compared to control and 10 mg Cu/kg DM treatments. These results suggest that increasing dietary Cu concentration to 20 mg supplemental Cu/kg DM alters ruminal Cu solubility, redox potential, and VFA profiles. Further research is needed to determine whether an increase in the redox potential and a reduction in molar proportions of propionate can impact animal performance.