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

SIMPLE SUMMARY: Weaning is a stressful event for piglets reared under commercial conditions, often resulting in economic losses due to reduced animal performance and health. The growing discouragement of antibiotic applications under these circumstances has stimulated the search for alternatives, like plant-derived products, to sustain piglet health. Thymol, the main compound in thyme essential oil, is considered as a valid alternative, mainly due to its antimicrobial properties. However, upon ingestion thymol quickly disappears from the upper gastro-intestinal tract, so that the concentrations remaining in the distal small intestine are far too low to kill off undesired bacteria. We tested gluco-conjugation, the linkage of a compound with a glucose unit, as a protective measure to obtain elevated thymol concentrations in the gut. Therefore, weaner piglets were fed a basal diet either un-supplemented or supplemented with pure thymol or its gluco-conjugate, thymol α-D-glucopyranoside. Neither treatment could change the microbial composition. Nevertheless, thymol reduced diarrhea incidence and improved intestinal integrity, while thymol α-D-glucopyranoside did not. To conclude, gluco-conjugation insufficiently protected thymol from fast absorption and negated the positive physiological effects of thymol, indicating that further research is warranted. ABSTRACT: 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 log(10) 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.