Effects of Dietary Protease on Immune Responses of Weaned Pigs

This experiment was conducted to investigate effects of dietary protease on immune responses of weaned pigs. A total of 75 weaned pigs (7.06 ± 0.18 kg BW; 28 d old) were randomly assigned to three dietary treatments (5 pigs/pen; 5 pens/treatment) in a randomized complete block design (block = BW). The dietary treatments were 1) a diet based on corn and soybean meal to meet or exceed the requirement of crude protein as a positive control (PC; CP = 24.17%), 2) a low protein diet as a negative control (NC; CP = 23.51%), and 3) NC + 0.02% protease (PRO). The protease used in this experiment was a commercial product (Ronozyme® ProAct, DSM nutrition products, Kaiseraugst, Switzerland) containing 75,000 protease units/g derived from Bacillus licheniformis. The dietary treatments did not include spray dried plasma, fishmeal, zinc oxide, and antibiotics to avoid their antibacterial or physiological effects. Pigs were fed each treatment for 6 weeks. Blood was collected from randomly selected one pig in each pen on d 1, 3, 7, and 14 after weaning. Measurements were number of white blood cells (WBC) by an automated hematology analyzer calibrated for porcine blood and Tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), and C-reactive protein (CRP) by the enzyme-linked immunosorbent assay. Data were analyzed using the PROC GLM procedure of SAS. The statistical model for every measurement included dietary effect and BW as a covariate. Pigs fed PRO had lower WBC on d 7 (14.84 vs 20.42 × 10³/μL; P < 0.05) and TNF-α on d 7 (618 vs 889 pg/ml; P = 0.085) and 14 (437 vs 576 pg/ml; P = 0.069) than those fed NC, but there were no differences on WBC and TNF-α between PC and PRO. Pigs fed PRO had lower TGF-β on d 3 (630 vs. 1,588 and 1,396 pg/ml; P < 0.05) than those fed PC and NC. However, no differences were found on CRP among dietary treatments. In conclusion, addition of protease may reduce inflammatory responses of weaned pigs.