Effects of different doses and preparations of zinc oxide in weanling piglets on performance, intestinal microbiota and microbial metabolites

For years, high zinc levels (up to 3000 mg/kg feed) have been used to aid piglets during the weaning phase. However, studies revealed drawbacks like antimicrobial resistance and environmental impact. Since 2022, the EU limits zinc inclusion levels to 150 mg total zinc per kg. Therefore, alternative strategies for replacing high levels of zinc are of great interest. This study compares a potentiated zinc oxide source (HiZox®) and feed grade zinc oxide at various levels on piglet performance, fecal consistency and fecal microbiome. The trial involved a total of 1,440 healthy weaned piglets (DanBred × Duroc; 50% barrows, 50% gilts; initial BW 10.1 ± 1.46 kg) over the 28-day duration of the experimental period. Piglets were randomly assigned to 12 treatment groups, each consisting of 12 pens, with 10 piglets per pen. The trial comprised two periods: the starter period (days 1 to 14) focused on comparing the two zinc products, while all animals received a diet supplemented with 150 mg/kg of potentiated ZnO in the grower period (days 15 to 28). Treatment groups receiving feed grade ZnO were denoted as Z150, Z300, Z600, Z900, Z1500, and Z3000, while corresponding groups with the potentiated ZnO product were labeled H150, H300, H600, H900, H1500, and H3000, respectively. Body weight (BW) and feed intake (FI) were measured for every pen at days 1, 14 and 28. Fecal samples were collected on the same days. During the starter phase (days 1 to 14), potentiated ZnO significantly improved average daily gain (ADG) compared to feed-grade ZnO (P ≤ 0.001), with the highest values observed at 3000 mg/kg (H3000: 247 g/d vs. Z3000: 233 g/d). Feed intake (FI) was also higher in potentiated ZnO groups (P ≤ 0.001), and feed conversion ratio (FCR) was more efficient (e.g., H3000: 1.2 vs. Z3000: 1.24; P = 0.001). In the grower phase residual effects from the starter phase persisted: animals previously fed potentiated ZnO had improved FCR (P = 0.003). Fecal microbiota analysis revealed that higher zinc levels reduced Lactobacillus abundance (P ≤ 0.001) and increased the presence of genera typical of adult pigs, such as Clostridium sensu stricto 1 and Terrisporobacter (P < 0.01). In conclusion, based on the observed shift in fecal microbiota composition characterized by a reduction in lactobacilli and an increase in proteobacteria due to heightened dietary zinc levels, it is advised to adjust zinc supplementation to 150 mg/kg after the initial 2 wk post-weaning.