Is your horse lame? If the vet came and consulted a diagram of the Zodiac horse and then told you he could not bleed the hoof of the lame leg because the moon was in Pisces what would you think? Well, if you were living in the 12th Century you would have thought he was a very wise veterinarian. I recently found some very interesting information about veterinary practice in Medieval times in Kathleen Walker-Meikle’s book “The Horse Book; Horses of Historical Distinction.” Here is what she says.
“In the Middle Ages, Galenic humoreal theory (which stated that to achieve health one needed to balance the four humours in the body: black bile, yellow or red bile, blood and phlegm) and medical astrology ( where planets and stars were believed to influence the body) were applied to veterinary medicine. Blood letting was a commonly used technique to restore ‘balance’ if a horse was ill.
The zodiac horse is an image that replicates a similar popular iconographic scheme for humans. It was used by veterinary practitioners to judge when and when not to bleed a horse. The sky was divided into twelve sections, each ruled by one of the twelve signs of the zodiac. When the moon was in a particular zodiac, the horse was not to be bled in the part of the body ruled by that zodiac sign. For example, if the moon was in Aries, the horse’s head should not be bled, if the moon was in Pisces, the hooves should not be bled, and similarly, if the moon was in Cancer, the area around the shoulders should not be bled.”
HorseAddict 
I’d love to hear from you!