An Escherichia coli-derived phytase can fully replace inorganic phosphorus in maize–soybean meal diets for growing-finishing pigs

A total of 396 gilts (PIC 337 × C22 [synthetic white-line dam], 22.4 ± 2.3 kg body weight) was used in a four-treatment trial to investigate the effect of two phytase utilization strategies on growth performance, bone ash and nutrient excretion. Pigs were housed in an environmentally controlled building that contained multiple manure pits. Three contiguous pens housing 11 pigs each were located above each pit. Pens were weighed individually and an average weight for each pit was calculated. Blocks of three pits were then formed based on body weight and randomly allotted to dietary treatments, totaling three pits (nine pens) per treatment. Dietary treatments included (1) a phosphorus (P)-adequate maize–soybean meal control diet (PC), (2) PC less 1.3 g inorganic P (iP)/kg (NC), (3) NC plus 500 FTU phytase (OptiPhos, Phytex LLC)/kg, and (4) a diet devoid of iP with phytase supplemented to meet the P requirements of the pigs. Thus, phytase levels of 1000, 500 and 300 FTU/kg were supplemented from 22 to 49, 49 to 91 and 91 to 130 kg body weight, respectively. The P-releasing values utilized for 300, 500 and 1000 FTU/kg phytase were 1.0, 1.3 and 2.0 g/kg, respectively. Bone ash (metacarpals III and IV; g/100 g and g) was measured on one pig per pen at approximately 74 kg and on three pigs per pen at the end of the trial. Overall, pigs fed the NC diet tended to have lower (P<0.10) weight gains than the other pigs. Additionally, pigs fed the diet devoid of iP with graded phytase supplementation tended to have greater (P<0.10) gain/feed ratios than pigs fed the P-adequate diet. Bone ash (g and g/100 g) was highest (P<0.05) for control and NC + phytase pigs, whereas the NC pigs had the lowest (P<0.05) values, regardless of sampling time. Overall, P excretion was reduced (P<0.01) by 69 g/100 g from pigs fed the diet devoid of iP with graded phytase utilization. Complete replacement of iP with an E. coli-derived phytase maintained growth performance in growing-finishing gilts when diets were formulated to a similar available P concentration using accurate P-releasing efficacy estimates for phytase.