Toxic Essential Oils - dogs and large farm animals
Aniseed, Birch, Bitter Almond, Boldo, Calamus, Camphor, Cassia, Chenopodium, Clove, Crested Lavender, Garlic, Goosefoot, Horseradish, Hyssop (except decumbens variety), Juniper (except Juniper Berry), Mugwort, Mustard, Oregano, Pennyroyal, Red and White Thyme, Rue, Santalina, Sassafras, Savory, Tansy, Terebinth, Thuja, Wintergreen, Wormwood and Yarrow.
This is not an exhaustive list and there will be other oils out there that are toxic. Always double check and confirm with a vet if in doubt.