Dietary supplementation with coated zinc oxide enhanced growth performance by modulating systemic immunity and microbial composition in weaned pigs

Dietary zinc oxide (ZnO) is widely adopted in the swine industry to alleviate post-weaning diarrhea and promote the growth performance of weaned pigs. However, its low rate of absorption in the gastrointestinal (GI) tract leads to excessive excretion, which causes severe environmental pollution. To overcome this limitation, dietary coated ZnO (CZO) has been studied to enhance zinc absorption and mitigate its environmental influence. In the present study, we investigated the effects of dietary CZO on growth performance, frequency of diarrhea, nutrient digestibility, hematological and immune responses, and fecal microbiota of weaned pigs. A total of 72 weaned pigs [7.30 ± 0.01 kg of average initial body weight (BW); 28 days old] were randomly assigned to three dietary treatments (4 pigs/pen; 6 replicates/treatment): basal weaner diet (CON), CON with 2,500 ppm of ZnO (HZO), and CON with 200 mg/kg of coated ZnO (CZO). The experiment was conducted for 6 weeks. The CZO group increased (<italic>p </italic>&lt; 0.05) average daily gain and gain to feed ratio and showed tendency to reduce (<italic>p </italic>= 0.094) the frequency of diarrhea compared with the CON group during the first two weeks after weaning. The CZO group showed a tendency for the lowest levels of serum tumor necrosis factor-α (TNF-α) (<italic>p </italic>= 0.072) on day 7 and hematocrit (<italic>p</italic> = 0.083) on day 14 and the highest (<italic>p </italic>= 0.072) levels of the immunoglobulin M on day 14 among the treatment groups. The HZO group tended to have the lowest (<italic>p </italic>= 0.078) serum cortisol levels on day 7 among all treatments. At the genus level of gut microbiota analysis, the dietary CZO group showed a higher (<italic>p </italic>&lt; 0.05) relative abundance of <italic>Prevotella, Eubacterium, and Lactobacillus </italic>than pigs treated with the CON diet. The HZO group showed a higher (<italic>p </italic>&lt; 0.05) relative abundance of <italic>Eubacteirum</italic> and <italic>Lactobacillus </italic>than the CON group. Our results demonstrated that dietary CZO supplementation enhanced growth performance and reduced the incidence of diarrhea by modulating systemic immune responses and shifting fecal microbial compositions in weaned pigs, suggesting its potential as an alternative to the high dose ZnO diets.