Yeast-derived mannan-rich fraction as an alternative for zinc oxide to alleviate diarrhea incidence and improve growth performance in weaned pigs

The objective of this study was to evaluate whether partial or complete replacement of zinc oxide (ZnO) with the mannan-rich fraction (MRF) would maintain or further improve growth performance, and affect diarrhea incidence, nutrient digestibility, serum growth-related hormone level, and intestinal health in weaned pigs. A total of 192 weaned pigs (96 barrows and 96 gilts) with an initial body weight (BW) of 7.84 ± 0.75 kg were randomly assigned to four dietary treatments in a completely randomized block design. The dietary treatments included a basal diet without antibiotics or zinc (Zn) supplementation (CON), ZnO diet (CON + 1600 mg Zn/kg from ZnO), MRF diet (CON + 800 mg MRF commercial product/kg) and MFLZ diet (CON + 800 mg MRF commercial product/kg and 800 mg Zn/kg from ZnO). Pigs fed the MFLZ diet showed greater (P < 0.05) average daily feed intake (ADFI) during day 14–28, while pigs fed MRF and MFLZ diets tended (P = 0.094) to have greater average daily gain (ADG) during the overall period (day 1–28) compared with pigs fed the CON diet. Diarrhea incidences in ZnO, MRF, and MFLZ groups were lower (P < 0.01) than those in the CON group throughout the experiment. Except for the apparent total tract digestibility (ATTD) of crude protein (CP) in the MFLZ group, the ATTD of dry matter, organic matter, gross energy, and CP was greater (P < 0.05) in both MRF and MFLZ groups. Pigs fed MRF and MFLZ diets had greater serum IGF-I levels (P < 0.05) than pigs fed CON and ZnO diets on day 14. However, ZnO supplementation in diets did not affect nutrients digestibility and serum IGF-I level. Pigs fed ZnO, MRF and MFLZ diets had higher (P < 0.05) acetic acid concentrations in the cecum, while pigs fed the MFLZ diet had higher butyric acid concentrations in the colon compared with those fed the CON diet. Moreover, pigs in the MRF group showed higher (P < 0.05) microbial richness and diversity than pigs in the ZnO group. In conclusion, ZnO and MRF alone or combination positively impacted intestinal health, thereby alleviating diarrhea incidence and improving growth performance in weaned pigs, with higher nutrient digestibility as seen with MRF supplementation.