Effects of zinc oxide and microbial phytase on digestibility of calcium and phosphorus in maize-based diets fed to growing pigs

An experiment was conducted to test the hypothesis that inclusion of Zn at a pharmacological level in diets fed to pigs affects apparent total tract digestibility (ATTD) of Ca and P and standardized total tract digestibility (STTD) of Ca. The second hypothesis was that inclusion of microbial phytase increases the ATTD of Ca and P and the STTD of Ca regardless of the concentration of Zn in the diet. Fifty-six growing barrows (15.4 +/- 1.9 kg average BW) were allotted to a randomized complete block design with 7 dietary treatments and 8 pigs per treatment. A maize-based basal diet was formulated with either 0 or 2,400 mg/kg Zn from ZnO and 0, 1,000, or 3,000 units of phytase (FTU) per kilogram. A Ca-free diet was used to determine basal endogenous losses of Ca. Experimental diets were fed for 13 d, and feces were collected from the feed provided from d 6 to 11 using the marker-to-marker approach; urine was also collected from d 6 to 11. Retention of Ca, ATTD of Ca, and STTD of Ca increased (P < 0.01) as the concentration of phytase in the diet increased and were less (P < 0.01) if ZnO was used than if no ZnO was added to the diet. Retention of P and the ATTD of P increased (P < 0.0001) as the concentration of phytase increased in the diet, but the increase was greater if ZnO was not added than if ZnO was added to the diet (interaction, P < 0.05). In conclusion, pharmacological levels of Zn reduced Ca and P digestibility and retention, but this effect was partly ameliorated by the inclusion of phytase in the diets. Inclusion of microbial phytase increased the ATTD and STTD of Ca in diets and also the ATTD of P.