In vitro phytase activity after steam conditioning and pelleting may not consistently correlate with in vivo measurements among commercial phytases

Abstract

Summary An experiment was conducted to evaluate correlations between in vitro phytase activity after pelleting and broiler performance, tibia mineralization, and plasma myo-inositol of broilers fed diets containing different phytase enzymes conditioned at 3 different temperatures (70°C, 80°C, and 90°C). Dietary treatments included a positive control (0.9% calcium [Ca] and 0.4% nonphytate phosphorus [nPP]) and negative control (NC; 0.7% Ca and 0.2% nPP) and 4 additional diets containing commercially available phytase products (A, B, C, and D) added to the NC based on analyzed activity and manufacturer's recommendations. Treatments were arranged in a 6 (diet formulation) × 3 (conditioning temperature) factorial in a randomized complete block design, with 10 replications of 10 male broilers fed each of 18 dietary treatments for 21 D. Correlations were determined with categorical and replicated data. A conditioning temperature × diet formulation interaction occurred for day 14 and 21 feed conversion ratio (FCR) and day 21 tibia ash (P 0.05), phytase C correlated with tibia ash mg/chick (P = 0.01, r = 0.46), and phytase D showed a moderate correlation with tibia ash mg/chick (P = 0.16, r = 0.26) and plasma myo-inositol concentration (P = 0.15, r = 0.27). This study did not demonstrate a common in vivo performance metric that was correlated with in vitro phytase activity after manufacture among commercial phytase products that decreased in activity because of increased conditioning temperature. Both in vivo and in vitro measurements should be assessed to properly evaluate the efficacy of an enzyme.