Objectives were to evaluate the effects replacing 40 ppm of zinc from zinc sulfate (CON) with zinc amino acid complex (Zn; Availa-Zn, Zinpro Corp., Eden Prairie, MN) on PMN function and acute phase protein production following an i.v. lipopolysaccharide (LPS) challenge in lactating cows. Cows were enrolled in a 2 × 2 factorial design and assigned to 1 of 4 treatments: (1) pair-fed (PF) control (PF-CON; 5 mL saline; n = 5), (2) PF Zn (PF-Zn; 5 mL saline; n = 5), (3) LPS-euglycemic clamp control (LPS-CON; 0.375 μg/kg BW LPS; n = 5), (4) LPS-euglycemic clamp Zn (LPS-Zn; 0.375 μg/kg BW LPS; n = 5). Prior to study initiation, cows were fed their respective diets for 42 d. During P1 (3 d), cows received their respective dietary treatments and baseline data was obtained. At the initiation of P2 (2 d), a 12-h LPS-euglycemic clamp was conducted or cows were pair-fed to their respective dietary counterparts. Mild hyperthermia (1°C, relative to PF cows) was observed in LPS cows at 3 h postbolus (P < 0.01). Throughout P2, rectal temperature of LPS-Zn cows was decreased (0.3°C), relative to LPS-CON cows (P = 0.01). Administrating LPS increased circulating LBP and SAA (3- and 9-fold, respectively), relative to PF cows (P < 0.01). Compared with LPS-CON, LPS-Zn cows had increased circulating SAA (38%) 24 h postbolus (P = 0.03). Ionized calcium was decreased (33% at 12h) post-LPS administration and dietary Zn tended to alleviate this response (P = 0.10). Compared with PF cows, circulating WBC and neutrophil counts initially decreased, then gradually increased (P < 0.01). Relative to baseline, oxidative burst of LPS-Zn cows was increased (44%; P = 0.05) throughout P2 and tended to be increased (31%; P = 0.07) in LPS-CON cows. Myeloperoxidase released after in vitro stimulation increased in all treatments at 12 h postbolus. Throughout P2, myeloperoxidase was increased in LPS-CON and tended to be increased in LPS-Zn cows, relative to baseline (37 and 22%, respectively; P < 0.01 and P = 0.09). In summary, supplemental Zn increased circulating SAA, reduced fever, and tended to alleviate hypocalcemia following immunoactivation, but appeared to have little or no effect on PMN function.