Chinese Herbal Medicines as Natural Alternative Products to Antibiotics in Weaned Piglets through Intestinal Microbiota Regulation

During the growth process of weaned piglets, digestive problems such as gastrointestinal disorders and diarrhea are common. Farmers usually use antibiotics to help piglets grow smoothly. However, the overuse of antibiotics can lead to antibiotic resistance issues. Therefore, this study chose to use plant extracts as feed additives to explore their potential as alternatives to antibiotics. Additionally, Tilmicosin was used as the antibiotic because it is widely used in treating respiratory infections in piglets. Since traditional Chinese medicine often uses natural products, we selected Guizhi Li-Zhong (GLZ) extract as an alternative to antibiotics. The experiment involved 126 piglets, each 4 weeks old, which were randomly assigned to one of four groups: the sham group (basal diet without supplements, 10.3 ± 0.4 kg, n = 31), the low-dose GLZ group (basal diet with 0.05% GLZ, 10.9 ± 0.4 kg, n = 32), the regular-dose GLZ group (basal diet with 0.2% GLZ, 10.6 ± 0.4 kg, n = 32), and the regular-dose Tilmicosin antibiotic group (basal diet with 0.2% Tilmicosin, 10.2 ± 0.3 kg, n = 31). We recorded and compared the survival rate, growth rate, feed conversion ratio, and diarrhea incidence among four groups of weaned piglets from the 4th to the 10th weeks of age. Then, we examined the oxidative stress, inflammation, and apoptosis in small intestine tissue (jejunum and ileum) through immunohistochemistry and Western blot and compared the gut microbiota in large intestine tissue (colon and rectum) through a next-generation sequencing (NGS) analysis. Our results showed that weaned piglets supplemented with 0.05% and 0.2% GLZ had better survival rates, growth rates (p < 0.01), and feed conversion ratios (p < 0.01) compared to those receiving sham treatment. Even weaned piglets supplemented with 0.2% GLZ performed better than those supplemented with 0.2% Tilmicosin antibiotics (p < 0.05). Furthermore, the incidence of diarrhea and small intestine injury (indicated by oxidative stress-, inflammation-, and apoptosis-related proteins) in piglets supplemented with 0.05% and 0.2% GLZ was lower than in piglets receiving sham treatment (p < 0.05). Even piglets supplemented with 0.2% GLZ had less injury than those supplemented with 0.2% Tilmicosin antibiotics (p < 0.05). The NGS results further showed that GLZ treatment significantly improved beneficial bacteria in weaned piglets (p < 0.05), while antibiotic treatment reduced beneficial bacteria (p < 0.05). In summary, we recommend adding GLZ to the feed as an alternative to antibiotics. This not only effectively reduces intestinal damage but also improves the gut microbiota, thereby promoting the growth of weaning piglets.