APPARENT DIGESTIBILITY OF PROTEIN AND AMINO-ACIDS IN BROILER-CHICKENSFED A CORN-SOYBEAN DIET SUPPLEMENTED WITH MICROBIAL PHYTASE

The effect of microbial phytase supplementation on CP and amino acid ( AA) digestibility was investigated in a 28-d trial using 360 sexed, da y-old broiler chickens fed corn-soybean meal diets. The experimental d esign was a completely randomized one with a 3 x 2 factorial arrangeme nt of treatments. The variables included P and Ca levels and phytase: P and Ca levels were: normal P-normal Ca [0.45% available P (P-a), 1.0 % Ca], low P-normal Ca (0.35% P-a, 1.0% Ca), and low P-low Ca (0.35 P- a and 0.6% Ca); and phytase at 0 and 600 U/kg diet. Phytase supplement ation increased body weight gain (P < 0.014) and feed intake (P < 0.00 4) at 19 d in male chickens; in females, phytase increased (P < 0.012) only body weight gain at 19 d. The low P-normal Ca diet reduced (P < 0.05) feed intake and body weight gain in both sexes at 7, 14, and 19 d, compared to the normal P-normal Ca diet; the reduction of Ca in the low P diet prevented the above depression, resulting in body weight g ain and feed intake to a level comparable to that of the normal P-norm al Ca diet. Microbial phytase supplementation had no effect (P < 0.065 ) on the apparent ileal digestibility (AID) of CP or any AA except Met and Phe in male broiler chickens. In females, adding phytase increase d the AID of all AA except Lys, Met, Phe, and Pro. The low P-normal Ca diet reduced (P < 0.05) the AID of Phe, Asp, and Ser in male chickens and reduced the AID of all the AA except Met and Pro in females compa red to the normal P-normal Ca diet. The reduction of Ca in the low P d iet prevented the depression of the AID of the AA caused by the low P- normal Ca diet, resulting in AID of AA having a level comparable to th at of the normal P-normal Ca diet in both sexes. Phytase supplementati on did not have any effect (P > 0.05) on apparent ''fecal'' digestibil ity (AFD) of CP or any of the AA in male chickens; however, in female chickens it increased the AFD of Thr, Asp, Glu, and Ser. In summary, p hytase supplementation increased growth performance in both sexes; inc reased AID and AFD of most of the AA, particularly in female chickens. The optimum growth performance and AA digestibilities were obtained w ith the lowest input of resources, in the low P-low Ca diet supplement ed with microbial phytase.