Objectives were to evaluate effects of maintaining eucalcemia on production and immunity following an i.v. lipopolysaccharide (LPS) challenge in lactating cows. Cows were enrolled in a study containing 2 experimental periods (P); during P1 (3 d), cows consumed feed ad libitum and baseline values were obtained. At the initiation of P2 (4 d), cows were assigned to 1 of 2 treatments: (1) LPS administered (LPS-CON; 0.5 μg/kg of BW LPS; n = 6) and (2) LPS administered + eucalcemic clamp (LPS-Ca; 0.5 μg/kg of BW LPS; Ca infusion; n = 6). Effects of treatment, time, and treatment by time interaction were assessed using PROC MIXED (SAS Inst. Inc., Cary, NC). Cows were fasted for 12 h during P2. After LPS administration, ionized Ca (iCa) was determined every 15 min for 6 h and every 30 min for an additional 6 h and Ca infusion was adjusted in LPS-Ca cows to maintain eucalcemia. Blood iCa was decreased 32% for the first 12 h post-LPS in LPS-CON cows, and by design Ca infusion prevented hypocalcemia. Collectively, 12 ± 0.9 g of Ca was infused to maintain eucalcemia. Mild hyperthermia (0.8°C) was observed for ~6 h post-LPS administration, relative to P1. From 6 to 7 h post-LPS rectal temperature of LPS-Ca cows was increased (0.6°C), relative to LPS-CON cows (P < 0.01). Overall, DMI did not differ due to treatment, but hypophagia was observed for 2d post-LPS, relative to baseline (34 and 45% for LPS-CON and LPS-Ca, respectively; P < 0.01). On d 1 of P2, milk yield decreased (61%) in both treatments relative to P1, however, the decrease tended to be more pronounced with Ca infusion (15%, relative to LPS-CON cows; P = 0.07). Overall circulating LPS-binding protein (LBP) continuously increased post-LPS, at 24 h circulating LBP in LPS-Ca cows increased (68%), relative to LPS-CON cows. While not significant (P = 0.28), circulating SAA was numerically increased (47%) in LPS-Ca cows throughout P2, relative to LPS-CON cows. Neutrophil counts of LPS-Ca cows were reduced from 9 to 12 h post-LPS, relative to LPS-CON cows (P = 0.03). In summary, maintaining eucalcemia during an immune challenge decreased milk yield and neutrophil counts whereas rectal temperature and circulating LBP increased.