The experiment was carried out on 32 Polish Landrace x Large Polish White sows, mated Pietrain boar, over pregnancy and lactation (28 days) divided into 4 groups, 8 animals each. The animals received the same, cereal-soybean meal based full-feed mixture but deficient in P and Ca. The treatments differed in feed additive: C – control (without any additive), MP – microbial phytase (500 PU kg^-1 mixture), Ca – citric acid (20 g kg^-1 mixture) ang MP+CA treatment – both phytase and citric acid additives. The apparent total tract digestibility (Cr₂O₃) was determined on weeks 8 and 14 of pregnancy and week 3 of lactation and, after accomplishing 28-day lactation – the apparent ileal digestibility of organic matter, protein and amino acids. The additive of microbial phytase increased (p≤ 0.05) the apparent total tract and ileal digestibility coefficients of organic matter, crude protein and some amino acids. The best results were noted when phytase was supplemented together with citric acid, although the increase, in comparison with phytase added solely, was not significant. Citric acid only sightly, statistically in significantly, elevated the investigated coefficients.

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