The application of phytase in conventional dry swine diets has been shown to improve P availability and utilization. The effectiveness of phytase may be further improved by steeping feedstuffs with phytase before feeding. A study was conducted to determine the value of steeping high-moisture corn (HMC) with phytase in P-deficient liquid diets for starter pigs. A total of 384 pigs were weaned at 19 to 23 d of age and 6.7 kg of BW. Pigs were randomly assigned to pens, with 8 barrows and 8 gilts per pen and 5 pens per dietary treatment (only 4 pens for the control treatment). The 5 dietary treatments (all HMC-based 3-phase feeding programs) were 1) negative control with no added phytase, 2 and 3) negative control with phytase added to the HMC to achieve 62.5 or 125 phytase units (FTU)/kg of HMC (DM basis) of phytase added to the HMC and allowed to steep for 24 h before feeding, and 4 and 5) negative control with the same amount of phytase added to the base mix without steeping before feeding. Total P content (88% DM basis) averaged 0.49% in phase I and 0.37% in phase II and III diets. Individual pig BW and per pen ADFI were measured on a weekly basis. Apparent total tract digestibility of DM, OM, CP, P, and Ca were measured using titanium dioxide as an indigestible marker in phase III diets. At the end of the study (7 wk postweaning), 4 pigs from each pen were killed for assessment of body composition, breaking strength and mineral content of metacarpals, total and soluble P content in duodenal digesta, and urinary P content. There was no effect of added phytase on ADG, ADFI, or G:F. The soluble P:total P ratio in duodenal digesta was increased with the addition of phytase. Steeping HMC with phytase resulted in greater digestibility of DM and CP. A trend toward increased digestibility of Ca with added phytase was observed, but there was no effect of dietary treatment on P digestibility. Urinary P content was considerably greater in pigs fed diets with exogenous phytase. Additional phytase resulted in increased P and Ca content in the empty body. Metacarpal content of P and Ca and breaking strength were improved with added phytase. Despite a lack of effect on P digestibility, added phytase improved retention of Ca and P in starter pigs fed P-deficient HMC-based liquid diets. There was little benefit from steeping HMC with phytase before feeding.

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