Characterization of the gut microbiome and resistome of piglets supplemented with low, moderate, and high concentrations of zinc oxide.

The livestock sector is standing out for its substantial use of antimicrobials but is also investing in the development of mitigation strategies. Supranutritional concentrations of zinc (Zn) are served to piglets to prevent post-weaning diarrhea. This practice is detrimental to the piglet's assimilation of nutrients and can impact the environment through the excretion of unassimilated Zn, contributing to the persistence of antibiotic resistance by co-selection. In this study, the ileum and colon microbiome of piglets fed low (175 ppm), moderate (953 ppm), or high (2,991 ppm) concentrations of zinc oxide for 21 days after weaning were investigated using metagenomics and 16S rRNA amplicon sequencing. The pH and volatile fatty acids (VFA) were measured in cecum and colon. The colon resistome was investigated using metagenomics and PCR. The high Zn supplementation led to an increase in pH and a decrease in the VFA in both the cecum and colon. The bacterial diversity in colon was negatively impacted by the high Zn diet, with thriving IMPORTANCE: Developing alternatives to antibiotics is imperative to mitigate the global antimicrobial resistance crisis, particularly within the livestock sector, the predominant consumer of these agents. Yet, interventions introduced without due consideration may precipitate unintended consequences. In North American swine production, supranutritional zinc supplementation in pig feed has been adopted to prevent post-weaning diarrhea and sustain profitability. However, excessive zinc disrupts iron and copper metabolism and perturbs mitochondrial homeostasis, impairing energy metabolism, antioxidant defenses, and innate immunity. Moreover, high dietary zinc increases the excretion of this heavy metal, contributing to environmental pollution and fostering antibiotic-resistant bacteria through co-selection. This study provides further evidence supporting the restriction of zinc supplementation to nutritional needs, as supranutritional diets compromised the fermentative capacity of the pig gut microbiome and increased the frequency of clinically relevant antimicrobial resistance markers.