Effects of Thymol and Thymol α-D-Glucopyranoside on Intestinal Function and Microbiota of Weaned Pigs

The present study evaluated gluco-conjugation as a measure to delay thymol absorption and enhance its antimicrobial activity in the gut of weaned piglets. The three dietary treatments consisted of a basal diet without additives (T_CON), supplemented with thymol at 3.7 mmol/kg dry matter (T_THY), or with an equimolar amount of thymol α-D-glucopyranoside (T_TαG). Each dietary treatment was replicated in 6 pens with 2 piglets per pen (n = 12 for analytical parameters) and was supplemented for 14 days. The total (free plus gluco-conjugated) thymol concentrations in the stomach contents were 14% lower in T_TαG as compared to T_THY piglets. Neither of the additives could be detected further down the gut. E.coli counts in the proximal small intestine were significantly lower in T_THY than in T_TαG pigs (3.35 vs. 4.29 log₁₀ CFU/g); however, other bacterial counts and their metabolites were unaffected by treatment. A metagenomic bacterial analysis revealed a great relative abundance of Lactobacillus spp. in the distal small intestine (range 88.4%-99.9%), irrespective of treatment. The intestinal barrier function was improved by T_THY, but not T_TαG, compared to T_CON. In conclusion, gluco-conjugation did not result in higher thymol concentrations in the gut, but conversely, it seemed to diminish the biological effects of thymol in vivo.