Increasing Microbial Phytase in Diets with Moderate and High Phytate on Nursery Swine Growth Performance

Abstract Supplementation of exogenous phytase at superdosing levels has resulted in improvements in growth performance of nursery and growing finishing swine. In this context, recent commercial scale research reported that 11-kg nursery pigs fed P deficient diets, containing 0.31% phytate P and supplemented with superdosing levels of phytase, resulted in improvements to growth performance, inositol release, and bone ash percentage. While a positive response to increasing phytase could be attributed to a reduction of phytate anti-nutritional effects, an increased nutrient digestibility, or inositol release, there is no clear understanding of the underlying mechanisms associated with this response. To elucidate these mechanisms, a total of 2,444 pigs (initially 12.2 kg BW) were used in a 20-d experiment. Pens of 34 to 36 pigs were randomly allotted to 1 of 4 dietary treatments with 17 to 18 replications per treatment. Dietary treatments were arranged in a 2 × 2 factorial with main effects of phytase concentration (PC) 765 or 3,060 FTU/kg (Allzyme Swine HC; Alltech, Inc., Nicholasville, KY) and dietary phytate concentration (DP) 0.27 or 0.31%. Pigs were fed a corn-soybean meal-based diet formulated to contain 1.30% SID Lys, 2,572 kcal/kg NE, 0.30% aP and 1:14 Ca:P. To increase DP concentration, experimental diets were supplemented with 7.5% canola meal. No significant PC × DP interactions (P 0.10) were observed in growth performance. From d 0 to 20, pigs fed diets supplemented with higher PC had greater (P = 0.050) ADG, without evidence for differences (P 0.10) in ADFI or G:F. Greater ADG observed in pigs fed higher PC resulted in marginally (P = 0.090) heavier final BW, despite of DP concentration. In conclusion, whereas pigs fed with higher PC improved ADG and BW, the lack of PC × DP interaction might suggest that inositol release is not driving the growth performance response, or inositol concentration is already abundant. Moreover, this data might also suggest that mechanisms such as nutrient digestibility improvements due to phytase supplementation also play a role in enhancing growth performance. Phytase superdosing might offer opportunities to improve growth performance beyond the early nursery phase.