Effect of Dietary Zinc Amino-Acid Complex Supplementation on Cattle Performance, Biomarkers of Inflammation and Metabolism, and Liver Abscess Formation in Steers Receiving a Mild Acidosis Challenge

The study objective was to evaluate the effect of dietary Zn supplementation on steer performance, biomarkers of inflammation and metabolism, and liver abscess formation in response to a mild acidosis challenge. Forty-two steers (417 ± 1.5 kg; n = 6/pen) were housed in pens with bunks designed to measure individual DMI and fed one of two diets containing either 0 (CON; n = 18) or 90 mg Zn/kg from a Zn-amino acid complex (Zn-AA; n = 18; AvailaZn) for 109 days. Six additional steers were fed the CON diet and did not undergo the acidosis challenge (NON; n = 6). The acidosis challenge included restricting steers to 50% of the previous 7 d daily DMI on d 47, and on d 48, steers were individually provided 10% of DMI as cracked corn (as-fed) at 0800 h followed by ad libitum feed access 2 h post-grain consumption. Steer was the experimental unit, and two contrasts were constructed: NON vs. CON and CON vs. Zn-AA. Blood samples were collected on d 40, 49, 53, 69, 80, and 108 and analyzed as repeated measures. Final BW and overall ADG (2.29, 2.30, and 2.31 ± 0.920 kg/d for CON, Zn-AA, and NON, respectively) were not different (P ≥ 0.74) between treatments. By design, DMI was greater (P < 0.01) for NON compared to CON on d 47 but was not different (P ≥ 0.41) for the remainder of the experiment. While HCW (423, 428, and 424 ± 7.9 kg for CON, Zn-AA, and NON, respectively) and ribeye area were not different (P ≥ 0.53) due to treatment, marbling score tended (P = 0.06) to be greater in CON compared to Zn-AA. The 12^th rib backfat thickness was greater (P = 0.05) in NON vs. CON steers. Liver abscess incidence was not different (P = 0.12) across CON (24% abscesses) and Zn-AA (6% abscesses). However, NON had a greater incidence (P ≤ 0.05; 50% abscesses) compared to CON. Overall blood fibrinogen and leukocyte counts were not different between treatments (P ≥ 0.67), but neutrophil-to-lymphocyte ratio tended to be greater in NON vs. CON (P = 0.08). Serum aspartate aminotransferase and gamma-glutamyl transferase concentrations were greater in NON vs. CON (P ≤ 0.02), and serum alkaline phosphatase concentration was lesser in CON vs. Zn-AA (P < 0.01). Overall, dietary Zn supplementation did not affect cattle performance in response to a mild acidosis challenge.