Effects of high inclusion of soybean meal and a phytase superdose on growth performance of weaned pigs housed under the rigors of commercial conditions.

Two studies were conducted to determine whether soybean meal (SBM) use in nursery pig diets can be increased by superdosing with phytase. In Exp. 1, 2,550 pigs (BW of 5.54 ± 0.09 kg) were used to evaluate the optimal level of phytase in low- or high-SBM diets. Two SBM levels (low and high) and 4 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. Pigs were fed a 3-phase feeding program, with each period being 10, 10, and 22 d, respectively. Inclusion of low and high SBM was 15.0 and 25.0%, respectively, for Phase 1; 19.0 and 29.0%, respectively, for Phase 2; and 32.5% for the common Phase 3 diet. Pigs fed diets with high SBM had improved G:F for Phase 1 and 2 and overall ( < 0.01) compared with low-SBM diets. Phytase quadratically improved G:F during Phase 3 and overall ( < 0.05), with the optimum phytase dose being 2,500 FTU/kg. High-SBM diets tended ( = 0.09) to decrease stool firmness (determined daily from d 1 to 10) only on d 2. In Exp. 2, 2,112 pigs (BW of 5.99 ± 0.10 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 Exp. 1. Three levels of SBM (low, medium, or high) and 2 phytase levels (600 or 2,600 FTU) were combined to create 6 dietary treatments in a 3 × 2 factorial arrangement. Inclusion of SBM was 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. The percentage of pigs removed for medical treatment linearly declined with increasing SBM levels ( = 0.04). High-SBM diets tended ( < 0.10) to decrease stool firmness during d 4 and 5 and high phytase tended ( < 0.10) to improve stool firmness on d 2 and 4. Analyzed PRRS titers in saliva samples collected on d 20 and 42 confirmed the PRRS status of the pigs; however, viral load was not impacted by dietary treatments ( ≥ 0.11). 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.