Point-of-care (POC) devices that veterinary practitioners can use to easily and rapidly measure blood ionized calcium (iCa) levels in cows immediately after withdrawing a blood sample on the dairy farm are needed. Aims of present studies was to compare the commercially available ion-selective electrode handheld iCa meter (bovine blood iCa checker) with the benchtop blood gas analyzer GEM premier 3500 and handheld analyzer i-STAT 1. Sixty-two paired-point whole blood samples were obtained from three cows with hypocalcemia experimentally induced by Na2-EDTA infusion. Whole blood samples were also obtained from the 36 cows kept on a farm in field conditions. The results using the bovine blood iCa checker correlated with those using the GEM premier 3500 and i-STAT 1. Bovine blood iCa checker was “compatible” with the GEM premier 3500 and i-STAT 1 because the frequency of differences between the measurements within ± 20% of the mean were 100% (65/65, >75%) and 90.8% (59/65, >75%), respectively. In the field trial, the blood iCa concentration measured by the bovine blood Ca checker was significantly positively correlated with that measured by the i-STAT 1 portable analyzer. Bovine blood iCa checker was “compatible” with the i-STAT 1 because the frequency of differences between the measurements within ± 20% of the mean was 100% (36/36, >75%). Results from these findings, the bovine blood iCa checker may be applied as a simplified system to measure the iCa concentration in bovine whole blood.