Antagonistic effect of increasing dietary zinc on the efficiency of microbial phytase on calcium, phosphorus, and zinc digestibility and status in pigs: a meta-analysis

Dietary zinc (Zn), phytate, calcium (Ca), and microbial phytase (PhytM) interact in the gastrointestinal tract of pigs, which determines the utilization of phosphorus (P), Ca, and Zn. Previous studies have assessed the impact of Zn and PhytM on Zn status by measuring apparent total tract digestibility (ATTD) of Zn and plasma Zn concentration in pigs, and some of these studies also measured P and Ca ATTD. The objectives of this meta-analysis were to quantify the effect of Zn, PhytM and their interactions on (1) digestible P and Ca content (g/kg diet) and (2) digestible Zn and Zn ATTD (%) and plasma Zn status. To investigate these objectives, an exhaustive literature search was made to create two sub-databases: (1) Ca-P database containing 52 treatments, from postweaning pigs and using pharmacological Zn doses (> 1 000 mg Zn/kg), and (2) Zn database of studies from postweaning and grower pigs with dietary Zn concentration < 250 mg/kg, containing 71 treatments on Zn ATTD and 50 treatments on plasma Zn concentration. Using the Ca-P database, mixed-effects models showed that increasing dietary Zn concentration decreased digestible P (P < 0.001) and tended to increase digestible Ca (P = 0.083) concentrations. It also reduced the positive effect of PhytM on digestible P (Zn × PhytM interaction, P < 0.01) and digestible Ca (Zn × PhytM interaction, P < 0.01). Studies within the Zn database showed that increasing dietary Zn content increased digestible Zn with a linear positive (P < 0.001) and quadratic negative component (P = 0.08) but increasing dietary Zn concentration decreased the positive effect of PhytM on digestible Zn (Interaction Zn × PhytM; P < 0.001). Dietary Zn (P < 0.001) and PhytM (P < 0.001) improved plasma Zn concentration; however, the response to PhytM was dependent on the dietary Zn level (Interaction Zn × PhytM; P < 0.001), highlighting the homeostatic regulation response of the animal. In conclusion, pharmacological dietary Zn supply (> 1 000 mg Zn/kg) to postweaning pigs decreased the ATTD of P and Ca. Moreover, the positive effect of PhytM on the digestible content of Zn, P, and Ca as well as on plasma Zn, was dependent on dietary Zn concentration.