Effects of Matched Compound Enzyme on Nutrient Utilization and Physiological Responses in Growing Pigs Fed a Corn–Soybean Meal or Diversified Diet

This study evaluated the responses of growing pigs to a matched compound enzyme in two feeding systems: a corn–soybean meal diet and a diversified diet. Two independent experiments were conducted, each using 80 pigs (Duroc × [Landrace × Yorkshire]; average body weight, 33.0 kg), which were assigned to two treatments in a randomized complete block design (RCBD) according to initial body weight and sex, with five replicate pens per treatment and eight pigs per pen. In Exp. 1, pigs were fed a corn–soybean meal diet without or with 0.02% compound enzyme formulated (including xylanase, β-glucanase, β-mannanase, cellulase and pectinase) for this diet type. In Exp. 2, pigs were fed a diversified diet without or with 0.02% compound enzyme (including xylanase, β-glucanase, β-mannanase, cellulase, pectinase, amylase and protease). The supplemental level of the compound enzyme was selected according to the substrate characteristics of each diet, especially the content of fibrous components, and was further aligned with the inclusion rate recommended for practical feed production. Growth performance, apparent total tract digestibility (ATTD), serum immune and inflammatory indices, jejunal digestive enzyme activities, and cecal microbiota were evaluated. In Exp. 2, the G:F was higher during days 15–28 (p < 0.05) and tended to increase the overall G:F (p = 0.06). In Exp. 1, dietary compound enzyme supplementation increased the ATTD of dry matter (DM), ether extract (EE), and gross energy (GE) on day 28 (p < 0.05), elevated serum immunoglobulin A (IgA) concentration (p < 0.05) on day 14, reduced serum concentrations of interleukin (IL)-1β, IL-6, and IL-8 on day 28 (p < 0.05), and increased jejunal amylase activity (p < 0.05). In Exp. 2, dietary compound enzyme supplementation increased the ATTD of DM, organic matter (OM), crude protein (CP), and GE (p < 0.05), and enhanced the activities of amylase and chymotrypsin on day 28 (p < 0.05). Enzyme supplementation reduced the abundance of Erysipelotrichaceae in Exp. 1 (p < 0.05) but increased the abundance of Chlamydiaceae in Exp. 2 (p < 0.05). In conclusion, matched compound enzyme supplementation improved nutrient utilization in both diet systems, but the response profiles differed. The diversified diet system showed clearer improvements in feed efficiency and protein-related digestibility.