Kill Them With Kindness

This book is a clean Cozy Mystery short story that does not contain foul language, sexual situations, witches, or paranormal events.
While celebrating the new windfall of her very expensive Hanoverian gelding, Rufus, the old barn cat, showed up sick. Holly then realized that she hadn't chosen a vet for the animals. One of her employees suggested that she use the local Veterinarian in Hill City.
Since Rufus was not showing any improvement after seeing the vet, Holly made a follow up appointment to have him checked out again. Upon their arrival she found the doctor dead.
Was the the Veterinarian's death from natural causes or could it have been murder?