The effects of phytase on growth performance and intestinal transit time of broilers fed nutritionally adequate diets and diets deficient in calcium and phosphorus.

Five experiments (Exp.) were conducted to determine the effects of phytase on growth performance and intestinal transit time in chicks fed nutritionally adequate diets and diets deficient in Ca and nonphytate P (nPP). In Exp. 1 and 2, chicks were fed a nutritionally adequate diet from 0 to 6 d or from 0 to 4 d posthatching; assay periods were 8 or 10 d; average initial BW were 98 or 79 g; and average final BW were 371 or 369 g, respectively. Treatments were replicated with 12 pens of 5 chicks each. Corn-soybean meal (C-SBM) diets were adequate in all nutrients except Ca and nPP where appropriate. The treatments were 1) C-SBM, 1.0% Ca, and 0.45% nPP; 2) C-SBM, 0.80% Ca, and 0.25% nPP; 3) Diet 1 + 600 phytase units/kg of diet; 4) Diet 2 + 600 phytase units/kg of diet. Experiments 3, 4, and 5 were conducted to determine the effects of phytase on intestinal transit time in broilers. Broilers were fed the same nutritionally adequate diet from 0 to 18, 27, or 23 d posthatching, and the assay periods were 7 d. Treatments were replicated with 18 individually penned broilers. Average initial BW were 768, 1,108, or 838 g, and average final BW were 1,299, 1,704, or 1,392 g in Exp. 3 to 5, respectively. Transit time data were collected on d 1 and 7 of the Exp. Diets were 1) C-SBM, 0.9% Ca, and 0.35% nPP; 2) C-SBM, 0.80% Ca, and 0.25% nPP + 600 phytase units/kg of diet. Transit time was calculated as the difference between the time feed was first ingested and the time of first appearance of solid feces. In Exp. 1 and 2, the reduction in dietary Ca and nPP reduced (P < 0.01) average daily gain (ADG), average daily feed intake (ADFI), and gain:feed. Phytase addition increased (P < 0.02) ADG and ADFI in diets deficient in Ca and nPP and in the nutritionally adequate diets. In Exp. 2, the reduction in Ca and nPP reduced (P < 0.01) toe and tibia ash percentage, but phytase addition increased (P < 0.01) toe and tibia ash percentage. The increase in toe ash percentage was greater in chicks fed the Ca and nPP deficient diet than in chicks fed the nutritionally adequate diet (Ca and nPP x phytase, P < 0.01). In Exp. 3, 4, and 5, transit time on d 1 was faster (P < 0.03) in chicks fed phytase. On d 7, transit time tended to be faster in chicks fed phytase, but the effect was not significant (P = 0.15). These data indicate that phytase increases ADG and ADFI in diets deficient in Ca and nPP and in diets formulated to be adequate (or excess) in all nutrients for broiler chicks. The increase in ADG and ADFI in chicks fed the nutritionally adequate diet may be due to a faster transit time of feed through the digestive tract, resulting in a greater feed intake and gain.