Improvements in sow productivity have raised questions regarding dietary mineral recommendations. Current calcium (Ca) levels and/or Ca sources might not support milk requirements of the larger litter in the modern sow. Therefore, four hundred and eighty mixed parity sows of a high prolificacy genetic line were used to evaluate the impact of the calcium source on the performance of highly prolific lactating sows. Sows were distributed in a completely randomized experimental design among six treatments containing different levels of inorganic Ca (INO) and organic calcium carbon-amino-phospho-chelate (CQT) inclusion. The sows were allocated to one of the six treatments represented by increased replacement ratios between sources of calcium: 100% INO; 100% CQT; 80% INO and 20% CQT; 60% INO and 40% CQT; 40% INO and 60% CQT; 20% INO and 80% CQT. Farrowing duration was not influenced (P>0.10) by the treatments, and averaged 185 minutes. Average daily voluntary feed intake did not differ (P>0.10) between treatments (5.54 kg d -1 on average). The lactation BW, backfat losses and chemical composition of body weight loss was not influenced (P>0.10) by the treatments. Litter size and average piglet weight at birth were not influenced (P>0.10) by the treatments (13.7 and 1.26 kg, on average). Litter weight gain, litter size and average piglet weight at weaning were also not influenced (P>0.10) by the treatments. The Treatments did not influence (P>0.10) estimated daily milk yield; which averaged 11.41 kg d -1 . The treatments tended to influence (P<0.10) urinary pH levels at day 7 of lactation, were 100% CQT sows had a lower pH value than other treatments (6.72 vs. 7.27). 100% CQT sows also showed a significantly lower pH level at d 14 and 21 when compared to the other treatments (6.44 vs. 7.09; P<0.05; and 6.48 vs. 7.14; P<0.01; respectively for d 14 and 21 of lactation). Free Ca and parathyroid hormone (PTH) serum levels were not affected (P>0.10) by treatments during lactation and averaged 1.38 mmol/L and 14.62 pg/ml, respectively. In conclusion, this experiment demonstrated that in diets for lactating sows an inorganic Ca source can be fully replaced by a more available Ca source (i.e., calcium carbon-amino-phospho-chelate), without negatively impacting the productive and reproductive performance of these animals or the performance of their litters.