This study compared different dietary calcium (Ca) to standardized total tract digestible phosphorous (STTD P) ratios and the use of microbial phytase on blood gases, electrolytes, and acid-base balance in pigs. Seven growing pigs (42.9 ± 2.2 kg) were equipped with portal vein catheters and assigned to five meals with different Ca:STTD P ratios: CTR - 2.6 Ca:STTD P ratio; C-Phy - 2.6 Ca:STTD P ratio + 750 phytase units (FTU)/kg; C-Phy+ - 2.6 Ca:STTD P ratio + 2,500 FTU/kg; LCa - 1.5 Ca:STTD P ratio; and L-Phy - 1.5 Ca:STTD P ratio + 750 FTU/kg. Portal blood samples were collected (2 experimental days per week) at 0, 2, 6, and 10 hours (hr) post-meal and analyzed for pH, partial pressure of carbon dioxide (pCO2), partial pressure of oxygen (pO2), bicarbonate (HCO3), base excess (BE), sodium (Na), potassium (K), ionized calcium (iCa), and glucose (GLU) concentrations. Data were analyzed as a 5x5 Latin Square design with repeated measures over time. Differences were considered significant at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10. Most parameters were not impacted by treatments (P ≥ 0.16) except that C-Phy tended (P > 0.07) to increase GLU compared to CPhy+. Although no treatment x time interaction was detected (P ≥ 0.16), the multiple comparison analysis shows that 10 hr after meal iCa was highest for C-Phy and lowest for LCa and L-Phy. Time effect was detected for most parameters (P ≤ 0.02). Blood pH and K were highest 2 hr after meal and lowest at 10 hr. Blood BE, HCO3 and GLU were lowest at 0 and highest at 2 hr after meal. Blood Na was highest at 0 and lowest from 2 hr after meal whereas pCO2 was lowest at 0 and highest from 2 hr after meal. Blood iCa was lowest 2 hr after meal but by 10 hr returned to baseline (0 hr). In conclusion, there are remarkable changes in blood gases, electrolytes, and acid-base balance during 10 hr after meal. Different Ca:STTD P ratios did not impact the blood acid-base balance despite the lower iCa in low Ca:P ratio diets
