Dietary iron and metal-based growth differentially modulate growth and gut microbiome of weaned piglets

Weaning-associated gut dysbiosis significantly contributes to increased susceptibility to enteric infections in postweaning pigs. While Fe, Zn and Cu are essential micronutrients for bacteria including pathogens, the exact effects of transition metal restriction and excessive exposure on gut dysbiosis and pathogen virulence during weaning transition remain unclear. This study investigated how dietary iron and pharmacological levels of zinc and copper affect dynamic changes of gut microbiota in postweaning piglets experimentally challenged with enteric pathogen. Fifty weanling pigs were stratified and randomized to five dietary treatments for 24 days (d). The experimental diets included a control diet (Con) containing 25, 139, and 141 mg/kg of Cu, Fe, and Zn, respectively, a low-iron diet (19 mg Fe/kg, LFe), a high-iron diet (1219 mg Fe/kg, HFe), a high-copper diet (257 mg Cu/kg, HCu), and a high-zinc diet (2631 mg Zn/kg with 2490 mg/kg from ZnO, HZn). The Con diet meets all nutrient requirements of nursery pigs, and the other diets were formulated based on the Con diet by removing or supplementing respective metals in mineral premix. All pigs were orally administered with enterotoxigenic E. coli (ETEC) once daily on d13–d16. Fecal microbiome was analyzed through 16 S rRNA sequencing on d1, 6, 12, 15, 18 and 24. Although the overall clinical signs of ETEC infection was moderate, the HFe and HCu pigs had lower diarrheal frequency than the Con pigs (P < 0.05). Fecal shedding of pathogen did not differ across treatments. Fecal microbiome showed the least changes in Shannon diversity in LFe pigs compared to the HFe and HCu groups over time (P < 0.05), while the HZn group showed the lowest Shannon diversity relative to groups Con, HFe, and HCu (P < 0.05). The β-diversity differed between LFe and HFe groups only at d24, whereas HZn reduced both α- and β-diversity beginning at d12 and d6, respectively (P < 0.05). Differential abundance analysis revealed greater abundance of Campilobacteria and Escherichia-Shigella in LFe pigs compared with the HFe group (P < 0.05), while HZn treatment was associated with Bacteroidota dominance and broad reductions in many taxa (P < 0.05). The pharmacological level of ZnO has profound effects on gut microbiome characterized by reduced diversity and Bacteroidota dominance. Despite moderate clinical signs, these results highlight the role of dietary iron and metal-based growth promoters in shaping gut microbiota and modulating resilience to infection.