Zoopharmacognosy (stems from Greek roots zoo "animal", pharmaco "drug/medicine" and gnosy "knowing”) is about animal self-medication and selecting their own plants, herbs, soils and berries etc for medicinal purposes.
Animals know exactly what they need and this is a natural instinct for them, they’re hard-wired for survival.
Horses will also select certain essential oils for inhalation, ingestion and topical use, always see what your horse self selects.