Zinc oxide quantum dots as an alternative to conventional ZnO: Physicochemical characterization and its application...

High-dose zinc oxide (ZnO) is effective in preventing diarrhea in piglets, but its use is limited by several concerns, including impaired intestinal barrier function, increased bacterial resistance, and the risks of heavy metal residues and environmental pollution. This study aimed to investigate whether zinc oxide quantum dots (ZnO QDs), a novel nanomaterial with diameters of less than 10 nm, could serve as an alternative to ZnO. In vitro, ZnO QDs were used to characterize the structure and evaluate antibacterial activity. In vivo, a total of 150 piglets (24 ± 1 d old, 7.45 ± 0.41 kg weight) were randomly divided into five groups: negative control group (CON), positive control group (ZnO; 1500 mg/kg Zn as ZnO), and 3 levels of ZnO QDs groups (250, 500, or 750 mg/kg Zn as ZnO QDs). Each group consisted of 10 replicates of 3 piglets for a 28-d trial. Results showed that ZnO QDs (size = 3.82 ± 0.38 nm, specific surface area = 17.65 m²/g) exhibited superior antibacterial activity in vitro due to their small size, large surface area, and high Zn release when compared to ZnO (size = 239.48 ± 78.02 nm, specific surface area = 0.91 m²/g). In vivo, the ZnO, ZnO QDs 250 and ZnO QDs 500 groups improved average daily gain (ADG; P = 0.003), while only the ZnO QDs 500 group decreased the feed to gain ratio (F/G; P = 0.038) compared with the CON group. Supplementation with ZnO QDs at 250 to 750 mg/kg also reduced diarrhea incidence in piglets (P < 0.05), with effects comparable to those observed with 1500 mg/kg ZnO. Dietary ZnO QDs supplementation mitigated Zn emissions and prevented hepatic Zn accumulation compared with high-dose ZnO (P < 0.001). Moreover, both ZnO QDs and ZnO improved the apparent digestibility of dry matter, organic matter, crude protein, and ether extract, enhanced digestive enzyme activities, and upregulated SGLT1 mRNA expression in the jejunal mucosa (P < 0.05). In addition, supplementation of 250 and 500 mg/kg ZnO QDs promoted jejunal development, and 500 mg/kg ZnO QDs increased microbial α-diversity indices and enriched beneficial bacteria such as norank_f_Muribaculaceae in the colon (P < 0.05). Conversely, high-dose ZnO hindered intestinal development and decreased Lactobacillus abundance and increased Escherichia-Shigella and Treponema abundances (P < 0.05), all of which are detrimental to the intestinal health of piglets. In conclusion, dietary ZnO QDs at 250 and 500 mg/kg effectively promoted growth, prevented diarrhea, reduced Zn emissions, improved nutrient utilization, and regulated gut microbiota, suggesting their suitability as an alternative to high-dose ZnO. This study provides a novel approach to prevent diarrhea in piglets.