Effect of Low-Phytate Corn and Phytase on Nutrient Excretion and Performance of Feedlot Cattle1

Two trials were conducted to determine the effect of microbial phytase (PHY) addition and low phytic acid (LPA) corn, on the nutrient digestibility and performance of growing beef steers. Four crossbred steers (initial BW = 345 ± 25 kg; Exp. 1) were used in a 4 × 4 Latin square design digestibility trial and were provided ad libitum access to 1 of 4 diets: 1) a normal corn and 15% corn silage diet (control diet), 2) diet 1 + PHY (control + PHY diet; 600 FTU/kg, where a FTU is the quantity of enzyme that liberates 1 µmol inorganic P/min from 0.005 mol/L sodium phytate at pH 5.5 and 37°C), 3) diet 1 with LPA corn replacing normal corn (LPA diet), and 4) diet 3 + PHY (LPA + PHY diet; 600 FTU/kg). Dietary P content was 0.38 to 0.40%, with no supplemental P added. Forty-eight crossbred steers (initial BW = 273 ± 6.9 kg; Exp. 2) were individually fed 4 diets: 1) a control diet; 2) a control + PHY diet; 3) diet 1 limit fed to 85% of ad libitum intake (limit-fed diet); and 4) the limit-fed diet + PHY. In Exp. 1, P digestibility, retention, and excretion were not affected (P > 0.05) by corn type or PHY. There was a trend (P < 0.10) toward increased N retention and decreased N excretion with PHY addition. In Exp. 2, overall, steers fed PHY in the diet had higher DMI (P < 0.03); however, PHY addition did not affect ADG or G:F. Inclusion of LPA corn tended to increase fecal Cu (P < 0.09) and S (P < 0.08) excretion (mg/d). Low-phytate corn and PHY supported similar performance and nutrient digestibility, but did not reduce P excretion in growing cattle diets.