Influence of the zinc to phytate ratio and superdoses of phytase on piglet growth performance

Abstract Text: Previous in vitro data indicates zinc (Zn) may bind to phytate at a Zn to phytate ratio of 4 to 1, which reduces Zn absorption. Phytase improves Zn absorption through the hydrolysis of phytate. An experiment was conducted to evaluate the Zn to phytate ratio and phytase supplementation (Quantum Blue) on piglet performance from weaning (d 0) to d 21. Pigs (5.2±0.9 kg; n=1280) were housed at 10 pigs/pen with 8 replicate pens/diet. Diets were arranged as a 2 x 4 x 2 factorial with 2 levels of phytate (analysed at normal, 0.50% or high, 0.67%), 4 levels of Zn from zinc oxide (ZnO; 0, 1000, 2000 or 3000 ppm) and 2 levels of phytase (0 or 2500 FTU/kg). Phytate was increased by the inclusion of 2.5% full fat rice bran and diets were formulated to meet the nutrient requirements of the pig (NCR, 1998), including calcium (0.86%) and available phosphorus (0.52%). This resulted in a Zn to phytate ratio ranging from < 1.0 to > 4.0 in the normal and high phytate diets as ZnO increased. Data were analysed as a factorial in JMP and significant means were separated using contrasts. There was no effect of Zn to phytate ratio on performance from d 0 to 21. ZnO supplementation increased ADFI from d 0 to 7 (quadratic P=0.05) and decreased ADFI from d 14 to 21 (linear P<0.02). ADG increased as Zn supplementation increased from d 0 to 7 (quadratic P<0.04). Zn supplementation improved FCR from d 0 to 7 (quadratic P=0.02) and from d 0 to 21 (linear P<0.03). Pigs fed high phytate tended to gain less than pigs fed normal phytate from d 7 to 14 (P<0.07) and d 0 to 21 (P<0.09). In addition, pigs fed high phytate were less efficient than pigs fed normal phytate from d 0 to 7 (P<0.03). Phytase improved ADG and FCR from d 0 to 7 (P<0.05), d 7 to 14 (P<0.05), and d 0 to 21 (P<0.05). In conclusion, small increases in phytate resulted in decreases in piglet ADG and FCR, thereby highlighting the anti-nutritive effect of phytate. Zn supplementation improved performance with a peak around 2000 ppm. However, there was no significant effect of Zn to phytate ratio on performance or phytase efficacy and phytase significantly improved ADG and FCR regardless of the level of phytate or Zn supplemented. 

Keywords: phytase, piglet, phytate