Can horses be bathed with dish soap?

Yes. but only a MILD dish soap.

The best brand to use is liquid Ivory dish detergent.

Mixing Ivory soap with Iodine is one of the best remedies for rain fot and other skin ailments. (Get your iodine from a tack shop or other place that sells supplies for farm animals. It comes in large bottles, is MUCH cheaper than buying the first aid type for humans and the iodine is stronger)

Here is a good recipe that I use all the time. (It's very popular with horse owners)

In a squeeze bottle, (I use the original Ivory dish soap bottle), mix 3 ounces of Iodine with 6 ounces of liquid Ivory dish detergent. (1 part iodine to 2 parts Ivory)

Thoroughly wet down your horse

Lather the full strength mixture onto your horse, using a sponge or "scrubby" plastic curry. Remember to be gentle

Allow to sit on the skin for at least 5 minutes.

And rinse WELL!

Your horse will be squeaky clean and super shiny!

**Note: Do a small "patch test" on light colored horses such as whites, greys, palominos, appaloosas, paints, etc to make sure the iodine doesn't stain their light hair/skin. (Especially if you're getting ready to show!) I personally have used this only on bays and chestnuts. Although I've never seen any staining on their white stockings, I'd recommend doing a patch test just be certain.