Apple Cider Vinegar is very good for your dog (and cat).
The first thing that apple cider vinegar (ACV) does for your dog is to keep their coat super shiny. By adding 1 tsp. to their water it will keep their fur healthy looking. ACV is high in potassium, a mineral that maintains the health of hair follicles.
It also works as a deterrent to fleas, naturally!
Here is a link for more information- http://earthclinic.com/Pets/acvfordogs.html