Investigation of nutritional and functional roles of β-mannanase on intestinal health and growth performance of nursery pigs fed low-cost formulated diets with high phytase inclusion

The objective of this study was to investigate the impacts of low-cost formulated diets (LCD) with high phytase inclusion on intestinal health and growth performance of nursery pigs, and roles of β-mannanase in mitigating these impacts. Thirty-six pigs (6.2 ± 0.2 kg initial body weight; BW) were individually housed and assigned to three dietary treatments in a randomized complete block design (n = 12 per treatment), with initial BW (light, medium, and heavy) and sex (barrows and gilts) as blocking factors. Pigs were fed for 42 d in three phases of 10, 10, and 22 d, respectively. The LCD contained 14% more soybean meal than the control diet (CON). Treatments included: 1) CON, 2) LCD, and 3) LCD with 800 TMU/kg of β-mannanase (LCD + β-mannanase), in which β-mannanase was added at the expense of corn. All diets were supplemented with 3,000 FTU/kg of phytase. On d 20 and 42, 18 pigs (n = 6 per treatment) were euthanized, and jejunal mucosa, jejunal tissues, and ileal digesta were collected. Experimental data were analyzed using the MIXED procedure in SAS, and differences were evaluated using preplanned contrasts (CON vs. LCD; LCD vs. LCD + β-mannanase). On d 20, the LCD increased (P < 0.05) the relative abundance (RA) of Christensenellaceae compared to CON. The LCD + β-mannanase tended to decrease (P = 0.060) the relative expression of jejunal toll-like receptor-4 (TLR4) compared to LCD. On d 42, the LCD increased (P < 0.05) the RA of Coriobacteriaceae, tended to increase (P = 0.073) jejunal interleukin-8 (IL-8) content, and decreased (P < 0.05) the apparent ileal digestibility (AID) of ether extract (EE) compared to CON. The LCD + β-mannanase decreased (P < 0.05) the RA of Coriobacteriaceae and jejunal interleukin-6 (IL-6) content and increased (P < 0.05) the AID of EE compared to LCD. The LCD decreased (P < 0.05) average daily gain (ADG) during phase 1, and reduced feed cost per BW gain during phases 1 to 3 compared to CON. The LCD + β-mannanase increased (P < 0.05) ADG during phase 1 and the feed cost per BW gain did not differ during phases 1 to 3 compared to LCD. In conclusion, the LCD increased jejunal IL-8, reduced ileal digestibility of EE, and decreased growth of nursery pigs, although the LCD reduced feed cost per BW gain compared to CON. However, β-mannanase supplementation mitigated negative impacts of the LCD by reducing jejunal IL-6, improving ileal digestibility of EE and growth, and maintaining similar feed cost per BW gain compared to LCD.