Botanicals have been proposed as a substitute for antimicrobials in swine diets because of their natural antibacterial activity. In the 1998 ISU Swine Research Report, peppermint (Mentha piperita), a botanical that grows in Iowa, was compared with a standard antibacterial nursery dietary regimen. Pig performance on all treatments was similar, including the positive and negative controls. At the tested inclusion levels (0, 0.5, 2.5, and 5.0%), peppermint displayed no advantage over the five-week nursery study compared with a “positive” control diet consisting of 50 g/ton Mecadox or with a “negative” control regimen containing no antibacterial inclusions. Increasing levels of peppermint did not influence the muscle characteristics evaluated.

This experiment evaluated Mecadox and 0, 0.5, and 1.0% peppermint levels under a similar feeding regimen, plus a 12-week post-nursery evaluation to observe any carryover effects. Peppermint failed to elicit a positive nursery response and those pigs performed less well statistically compared with the Mecadox-fed pigs. Pigs on the Mecadox diet maintained their advantage when cumulative performance was evaluated for the additional 12 weeks, but performance within each weighing period was not statistically different after the nursery phase. Under the conditions of this experiment, peppermint (as in the 1998 report) was not an efficacious addition to swine nursery diets meant to improve performance.