Thymol–Carvacrol (1:2) in Weaned Pigs: An In Silico–In Vitro–In Vivo Evaluation Linking Antibacterial Synergy, Microbiota Stabilization, and Performance Gains

Phytogenic feed additives, owing to their antimicrobial and anti-inflammatory properties, are emerging as promising tools to mitigate weaning stress in piglets. This study evaluated the mechanisms and efficacy of thymol and carvacrol in weaned pigs. Consensus blind docking was used to predict and verify swine molecular targets of thymol/carvacrol; Checkerboard assays quantified antibacterial effects of each compound alone and in combination against E. coli, Salmonella, S. flexneri , and Staphylococcus ; finally, a 28-day feeding trial was conducted with 100 weaned piglets (5 pens/group × 10 pigs/pen): the control received a basal diet, and the treatment diet was supplemented with 25 mg/kg thymol and 50 mg/kg carvacrol. Results showed that docking prioritized MAOA, MAOB, PTGS1, PTGS2, ESR1, and VDR as candidate targets. In vitro, the thymol–carvacrol combination was additive overall and synergistic against S. flexneri (1:2; ΣFICI = 0.38). In vivo, supplementation increased final BW at d 28 ( P  < 0.01) and ADFI and ADG during d 15–28 and d 1–28 ( P  < 0.05), with a trend toward lower F/G over the whole period ( P  = 0.09) and reduced early post-weaning diarrhea ( P  < 0.01). While cecal α-diversity was unchanged, β-diversity dispersion decreased by d 28 ( P  < 0.05). Serum DAO and ET decreased at d 28 ( P  < 0.05), and TNF-α was lower at d 14 ( P  < 0.05). Collectively, a 1:2 thymol:carvacrol blend appears to stabilize the intestinal microbiota and moderately modulate barrier and inflammatory responses, thereby lowering early diarrhea and improving late-phase and overall growth, supporting its feasibility as an antibiotic-free strategy for nursery pigs.