Two studies were conducted to determine whether soybean meal (SBM) use in nursery pig diets could be increased by superdosing with phytase. In the first experiment, 2,550 pigs weighing about 5.5 kg were used to evaluate the optimal level of phytase in low- or high-SBM diets. Two SBM levels and four phytase doses (0, 1,250, 2,500, and 3,750 phytase units [FTU]/kg were combined to create 8 dietary treatments in a 2 × 4 factorial arrangement. SBM inclusion rates of 15.0 and 25.0% were fed in Phase 1 (day 0-10); 19.0 and 29.0% for Phase 2 (day 11-20); and 32.5% for the common diet fed days 21-43. Pigs fed diets with high SBM had improved growth: feed (P ‹ 0.01) compared with low-SBM diets. Phytase quadratically improved feed efficiencies (P ‹ 0.05), with the optimum phytase dose being 2,500 FTU/kg.

In the second experiment, 2,112 pigs weighing about 6 kg were used to evaluate the impact of high levels of SBM and phytase on performance, stool firmness, mortality, and morbidity in weaned pigs originating from a porcine reproductive and respiratory syndrome (PRRS) virus–positive sow farm. Pigs were fed a 3-phase feeding program as in experiment 1. Three levels of SBM (low, medium, or high) and two phytase levels (600 or 2,600 FTU) were combined to create 6 dietary treatments. Inclusion rates of SBM were 15.0, 22.5, and 30.0% for Phase 1 and 20.0, 27.5, and 35.0% for Phase 2 for low, medium, and high SBM, respectively, and 29.0% for the common Phase 3 diet. Inclusion of SBM did not affect growth performance, however, the percentage of pigs removed for medical treatment linearly declined with increasing SBM levels (P = 0.04). Results indicate that SBM levels in early nursery diets can be increased without decreasing growth performance and may be favorable in pigs originating from PRRS-positive sow farms by reducing costs of medical treatments. Supplementation of phytase at superdose levels can improve growth performance independently from the level of SBM in the diet.