The effect of exogenous protease and soybean meal batches on growth performance and nutrient digestibility for broiler chickens

The thermal processing of soybean meal (SBM) can reduce its protein quality by decreasing solubility. Exogenous protease may help mitigate these negative effects on broiler chickens' protein digestibility. This study investigated how protease affects performance and digestibility in broiler chickens fed SBM from different batches selected from a commercial feed mill company. A total of 360 chickens from 14 to 26 days of age were randomly assigned in a 2 × 2 factorial arrangement with 2 SBM (batch A and batch B) and 2 protease doses (0 and 30 000 new feed protease units per kg of diet), totaling 4 treatments with 9 replicates and 10 birds each. The SBM samples were analyzed for proximate composition, protein quality indicators, color assessment, and microscopy images. From 19 to 21 days of age, excreta were collected to determine apparent total retention of DM, CP, and metabolizable energy. On day 26 of age, ileal content was collected to estimate the apparent ileal digestibility (AID) of DM, CP, amino acids, and digestible energy (IDE). Feed intake, BW gain, and feed conversion ratio were evaluated. Protein solubility in KOH was different for SBM from batches A and B. Total color difference demonstrated a noticeable change in SBM samples. Scanning electron microscopy images showed disorganized structures and asymmetric pores in particles from the SBM of batch A. However, insignificant pores and large cluster aggregates were observed in particles from batch B. No differences were found (P > 0.05) for feed intake and BW gain, whereas the feed conversion ratio was better for birds fed SBM from batch A (P < 0.05). SBM batches influenced (P < 0.05) AID of DM, CP, lysine, methionine, and IDE regardless of protease supplementation. Protease impacted the AID of CP and amino acids (P < 0.05) irrespective of the SBM, and no interaction was observed (P > 0.05), except for the AID of tyrosine (P < 0.05), which was greater for birds fed SBM of batch A plus protease. In conclusion, SBM from batch A presented higher values of KOH protein solubility and urease activity, as well as lower values, of trypsin inhibitor activity in comparison to SBM from batch B. In addition, protease inclusion improved CP and amino acid ileal digestibility regardless of the SBM batch.