BACKGROUND: The essential oils (EO) carvacrol, thymol, eugenol and trans‐cinnamaldehyde have well‐documented antimicrobial properties and offer therefore an alternative for the antimicrobial growth promoters in pig feeds. The aim of this work was to determine the degradation and kinetics of these EO along the gastrointestinal tract (GIT) of piglets, which is necessary information for correct application in pig feeds.

RESULTS: None of these compounds was significantly degraded in in vitro simulations of pig gastric fermentation. Carvacrol and thymol were not degraded in jejunal simulations, but significant losses of up to 29% were found in caecal simulations. Eugenol and trans‐cinnamaldehyde showed a more pronounced degradation in jejunal and caecal simulations. A single dose mixed with feed (13.0, 13.2, 12.5 and 12.7 mg kg⁻¹ body weight for carvacrol, thymol, eugenol and trans‐cinnamaldehyde respectively) was given orally to piglets. Half‐lives in total digestive tract ranged between 1.84 and 2.05 h, whereby trans‐cinnamaldehyde showed the fastest disappearance. All of these EO were mainly and almost completely absorbed in the stomach and the proximal small intestine. Plasma concentrations (sum of free and conjugated compound) peaked at 1.39, 1.35 and 0.83 h for carvacrol, thymol and eugenol respectively and this was accompanied by high concentrations in urine.

CONCLUSION: The four compounds were in vitro poorly degraded in the proximal segments of the GIT of piglets, but degradation is expected in more distal segments. In vivo, the EO were mainly and almost completely absorbed in the stomach and the proximal small intestine. Copyright � 2008 Society of Chemical Industry