Horse Tail for your large Dogs.
For more options for your companions. Create your fantasy animal in the Sims 4 with this Tail
Category / Tail
Long Mane: https://www.curseforge.com/sims4/pets/long-mane-unicorn-mane/
Short Mane: https://www.curseforge.com/sims4/pets/short-mane-unicorn-mane
Horse Hoof: https://www.curseforge.com/sims4/pets/hoof
Horse Head: https://www.curseforge.com/sims4/pets/horse-head