Assessing current phytase release values for calcium, phosphorus, amino acids, and energy in diets for growing-finishing pigs. Transl Anim Sci 2020;4:txaa034. [PMID: 32705032 DOI: 10.1093/tas/txaa034]

A time-series effect of phytase supplementation on phosphorus utilization in growing and finishing pigs fed a low-phosphorus diet

Two experiments were carried out to determine a time-series effect of phytase on phosphorus (P) utilization in growing and finishing pigs using growth performance, apparent total tract digestibility (ATTD) of nutrients, P excretion, and plasma concentrations of minerals as the response criteria for evaluation. In both experiments, treatments were arranged as a 3 × 4 factorial in a randomized complete block design with 3 corn-soybean meal-based diets including a P-adequate positive control (PC), a low-P negative control (NC; no inorganic P), and NC supplemented with phytase at 1,000 FYT/kg (NC + 1,000); and 4 sampling time points at days 7, 14, 21, and 28 in experiment 1, and days 14, 26, 42, and 55 in experiment 2. In both trials, 96 growing pigs with average body weight (BW) of 19.8 ± 1.16 and 49.8 ± 3.21 kg, respectively, were allocated to the 3 diets with 8 replicates pens (4 barrows and 4 gilts) and 4 pigs per pen. In experiment 1, pigs fed the PC had higher (P < 0.01) BW, average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed ratio (G:F) when compared with pigs fed the NC. There was an interaction (P < 0.01) between time and diet on the BW and ADG of pigs while a linear and quadratic increase (P < 0.01) was observed with the ADFI and G:F, respectively, over time. Phytase supplementation improved (P < 0.01) all growth performance responses. Pigs fed the PC had greater (P < 0.01) ATTD of P and Ca than pigs fed the NC. There was no interaction effect on the ATTD of nutrients. Phytase addition improved the ATTD of P and Ca over pigs fed the NC. There was an interaction (P < 0.01) between diet and time on the total and water-soluble P (WSP) excreted. There was a quadratic decrease (P < 0.01) in plasma concentration of Ca in pigs over time. In experiment 2, there was a quadratic increase (P < 0.01) in BW, ADG, and G:F of pigs over time. Similarly, the inclusion of phytase improved (P < 0.05) all growth performance parameters except ADFI. A linear increase (P < 0.05) in the ATTD of DM, P, and Ca occurred over time. Phytase inclusion improved (P < 0.01) the ATTD of P and Ca. Plasma concentrations of P were improved by phytase addition. Phytase supplementation of the NC reduced WSP excretion by 45%, 32%, and 35% over the growing, finishing, and entire grow-finish period, respectively. In conclusion, phytase improves the utilization of P in growing and finishing pigs; however, the magnitude of effect on responses may vary over time.

A comparison of the release of phosphorus by a phytase enzyme in pigs fed diets deficient or adequate in phosphorus content

Previous research indicated that phytase may release less phosphorus (P) from phytate when it is evaluated using diets with P levels above requirement as compared with diets below requirement. The objectives of this experiment were to further test the hypothesis that the P release values determined for phytase are higher when pigs are fed diets that are deficient (DE) in P compared with when they are fed diets that are adequate (AD) in P, and that phytase will increase the digestibility of dry matter (DM), gross energy (GE), nitrogen (N), and calcium (Ca) independent of dietary P status. Twenty-four barrows (body weight: 23.2 ± 1.8 kg) were randomly assigned to one of eight dietary treatments and housed in individual pens for 21 d and then moved to metabolism crates for 9 d, with the collection of urine and feces occurring on the final 5 d. A basal corn-soybean meal diet (P-AD) was formulated at 0.36% standardized total tract digestible (STTD) P and total calcium:STTD P (Ca:STTD P) of 2:1. A P-DE diet was also formulated to maintain a constant Ca:STTD P of 2:1 in both basal diets. Phytase was added to AD and DE diets at 350, 600, 1,000 phytase units (FYT)/kg. Pig was the experimental unit; diet (P-AD or P-DE), phytase level, and replicate were fixed effects. Orthogonal polynomial contrasts were used to test linear and quadratic effects of phytase within P-AD and P-DE diets. Phytase improved apparent total tract digestibility (ATTD) and STTD of P in both P-AD (linear P < 0.001) and P-DE diets (quadratic P < 0.001). Estimates for STTD P release were 0.07%, 0.09%, and 0.09% for 350, 600, and 1,000 phytase units (FYT)/kg in P-DE diets, and 0.02%, 0.03%, and 0.05% in P-AD diets, respectively. In P-DE diets, phytase improved absorption and retention of P and increased urinary excretion of P (quadratic P < 0.001). In P-AD diets, phytase improved absorption of P (linear P = 0.066), tended to improve retention (linear P = 0.066), and increased urinary excretion of P (quadratic P = 0.021). Phytase improved ATTD of Ca in P-DE diets (quadratic P = 0.002) but not in P-AD diets (P > 0.1). In conclusion, the release of P by phytase is lower in diets that are AD in P than those which are DE. Phytase increased the availability of Ca only in the diets DE in P. Finally, phytase increased the ATTD of DM and tended to increase the ATTD of energy, independent of dietary P status.