PSXIII-10 Effects of plant essential oil supplementation in low zinc, antibiotic-free diet on growth performance, blood parameters, and intestinal health of weaned piglets.

Abstract Weaning stress in piglets poses a significant challenge to the swine industry, often leading to compromised intestinal health, reduced feed intake, diarrhea, and increased mortality. Although antibiotics and pharmacological doses of zinc oxide have traditionally been used to alleviate these issues, rising concerns over antimicrobial resistance and environmental sustainability have driven the search for effective alternatives. The purpose of this study was to evaluate the effects of plant essential oils (PEO) as dietary supplements in a low-zinc, antibiotic-free diet on the growth performance, blood parameters, and intestinal health of weaned piglets. A total of 100 weaned piglets (7.90 ± 0.2 kg) were randomly assigned to five dietary treatments: ZnO, 0PEO, 30PEO, 60PEO, and 120PEO. Each treatment included four replicates of five piglets. The ZnO group received a basal diet (65 mg/kg Zn) supplemented with 1600 mg/kg zinc oxide from d 1 to 14 post-weaning. The 0PEO, 30PEO, 60PEO, and 120PEO groups received the basal diet with 0, 30, 60, and 120 mg/kg PEO, respectively. On d 28, one piglet per replicate with a body weight (BW) closest to the treatment average was selected and euthanized for sampling of duodenum, jejunum, and ileum tissue and colonic digesta (n = 4). Parameters included growth, serum indices, intestinal morphology, colonic volatile fatty acid (VFA), and colonic microbiota. Data were analyzed using SAS 9.4 (Cary, NC, USA). Polynomial contrasts were used to test the linear and quadratic effects of increasing PEO levels. A pre-planned contrast was used to compare the ZnO and 0PEO groups. Results showed a quadratic effect (P < 0.05) of PEO supplementation on hemoglobin concentration, with the predicted peak at 53 mg/kg. Villus height and the villus-to-crypt ratio in the duodenum, jejunum, and ileum increased linearly (P < 0.05) with PEO levels. Colonic VFA concentrations, including total VFAs, acetic, propionic, butyric, and valeric acids, were significantly affected by PEO in both linear and quadratic (P < 0.05) manners, with 52 mg/kg achieving total VFAs levels equivalent to the ZnO group. Additionally, colonic microbiota alpha diversity responded quadratically (P < 0.05) to PEO concentrations. In terms of growth performance, piglets in the 0PEO group had lower (P < 0.05) BW than those in the ZnO group by d 28. PEO supplementation showed a quadratic tendency (P = 0.055) on BW, with the highest estimated value at 69 mg/kg, comparable to that of the ZnO group. Although regression analyses identified slightly varying optimal PEO concentrations for different parameters, the 60 mg/kg level consistently improved multiple indicators. In conclusion, dietary supplementation with 60 mg/kg of PEO improved intestinal morphology, microbial fermentation, and growth performance, suggesting its potential as a natural alternative to pharmacological ZnO in antibiotic-free diets for weaned piglets.