The efficacy of an E. coli derived phytase on phosphorus (P) digestibility and excretion, on the form of the P excreted, and the optimal dietary calcium (Ca):P ratio was examined.
In experiment 1, 63 barrows (40.4 ± 1.9 kg) were assigned to receive one of 21 treatments arranged as a 3 × 7 factorial. Treatments consisted of three Ca levels (0.50, 0.60 and 0.70%) and seven phytase treatments [0, 250, 500, 1000 and 2000 FTU kg–1 of an E. coli-derived phytase and 500 FTU kg 1 of an A. niger phytase added to a P deficient (0.37% P) diet or 0 FTU phytase kg–1 added to a P adequate (0.53% P) diet].
In experiment 2, 144 pigs (6.52 ± 0.75 kg), received a P adequate (0.60% P) diet or a P deficient (0.44% P) diet supplemented with 0, 250, 500, 1000 or 2000 FTU phytase kg–1 for a 28-d trial. A subset of 36 barrows was then fed the same diets in a balance trial.
In experiment 3, 36 barrows (7.1 ± 0.75 kg) were assigned to one of six treatments arranged as a 2 × 3 factorial (0 or 500 FTU of phytase kg–1; 1.0, 1.6 or 2.2 Ca:P ratio).
In experiment 1, P digestibility improved from 21 to 54% with increasing phytase (quadratic; P < 0.05). Supplementing the diet with 500 FTU phytase kg–1 decreased the output of total and soluble P by 25% in experiment 2 and to a similar extent in experiment 3 at the lowest Ca:P ratio (P < 0.05). The effect of phytase on total P digestibility was mitigated as the dietary Ca:P ratio increased in exp. 3. Supplementation of swine diets with an E. coli derived phytase decreases output of total and soluble forms of P, but this effect is reduced at high dietary Ca:P ratios.