This study evaluated the effect of soybean meal (SBM) sources differing in trypsin inhibitor (TI) levels, with or without protease, in weaned pigs challenged with F18 E. coli. A low TI (LTI) SBM (2.2 mg/g TI, 43.3% CP, KOH 67.5) or a high TI (HTI) SBM (4.2mg/g TI, 47% CP, KOH 78) were added at 20%, resulting in a formulated difference of 0.40 mg/g in TI. A total of 90 barrows (17–19 days old, weighing 5.52 ± 0.32kg) were allotted to 30 pens. Each pen (except for unchallenged pigs) was randomly assigned to one of five treatments, including an unchallenged LTI (UCLTI), challenged LTI (CLTI), challenged HTI (CHTI), challenged LTI with protease (CLTIP), and challenged HTI with protease (CHTIP). The serine protease with keratinase activity (Cibenza DP100, NOVUS International Inc.) was included at 300 U protease activity/g of feed. All diets contained phytase (1,000 FTU), pharmacological zinc (1,500 mg/kg), and supplemental copper (150 mg/kg). After a 10-day acclimation period, all pigs in the challenged treatments were inoculated with F18 E. coli for two consecutive days. The period from days post-inoculation (dpi) 0 to 4 was defined as the infection phase, while dpi 4 to 11 was the recovery phase. Data were analyzed using Proc MIXED of SAS V9.4, contrasting the effect of UCLTI vs. other treatments, as well as the main effects of TI, protease, and their interaction using the challenged treatments. During the adaptation period, protease inclusion had no effect on ADG, ADFI, or G:F (P >0.10). Initial exposure to HTI resulted in a numerically higher ADFI (0.159kg vs. 0.138kg; P=0.12) but a decline in ADG (0.036kg vs. 0.060kg; P=0.03), leading to a lower G:F ratio (0.22 vs. 0.42; P< 0.01). During the infection period, diarrhea incidence increased from 2.8% in UCLTI to an average of 36.3% in the challenged treatments (P< 0.01), but UCLTI performance was not significantly different from that of the challenged treatments (P >0.10). Protease had no effect on performance during the infection period (P >0.10). However, HTI pigs had a higher ADFI than LTI pigs during infection (0.320kg vs. 0.394kg; P=0.05). During the recovery period, TI had no effect on performance (P >0.10). However, protease tended to improve ADG (0.293kg vs. 0.333kg; P=0.08) and G:F (0.49 vs 0.60; P=0.07). Furthermore, protease-challenged treatments resulted in ADG and G:F similar to UCLTI (0.334kg vs. 0.333kg and 0.60 vs. 0.67, respectively; P >0.10), whereas non-protease-challenged treatments had poorer G:F than UCLTI pigs (0.49 vs. 0.67; P< 0.05). These results demonstrate the negative effects of initial exposure to high TI levels. On the other hand, performance benefits of a serine protease with keratinase activity were observed during recovery from the F18 E. coli challenge, regardless of TI level.

Acosta, J., B. Lawrence, R. Qudsieh and D. Hancock. 2025. Protease improves feed conversion of weaned pigs recovering from experimental F18 E. coli challenge and fed soybean meal with different trypsin inhibitor levels. American Society of Animal Science 2025 Annual Meeting, Abstract 300