Figure 2.

Ionized calcium (iCa) concentrations in response to challenge and recovery from an EGTA/hypocalcemia challenge in multiparous, nonlactating, nonpregnant Holstein cows fed a negative dietary cation–anion difference (average −18.2 across all diets) for 21 d with low (LC; 0.45% Ca; n = 5), medium (MC; 1.13% Ca; n = 6) or high (HC; 2.02% Ca; n = 6) concentrations of dietary Ca. On days 22, 23, and 24, hypocalcemia was induced with an intravenous infusion of 5% EGTA in 2 different cows from each treatment daily. The LC treatment groups is represented by the solid circles, the MC treatment group by the open squares, and the HC treatment group by the solid triangles. (A) Ionized calcium (iCa) concentrations as measured by the Abaxis iSTAT in response to EGTA challenge. Line break at 145 min is representative of where of the slopes of the lines change. Prior to 145 min the slopes of the lines are different (P < 0.0001) and after 145 min the slopes of all the lines are equal (P > 0.05). (B) Ionized calcium (iCa) concentrations as measured by the Abaxis iSTAT during the recovery to EGTA challenge. (C) Ionized calcium (iCa) concentrations as measured by the Horiba LAQUAtwin Compact Calcium Ion meter in response to EGTA challenge. (D) Ionized calcium (iCa) concentrations as measured by the Horiba LAQUAtwin Compact Calcium Ion meter during the recovery from the EGTA challenge. All data are represented as the least square means ± standard error of the mean.