Concentrating on a time when anatomical studies were flowering, and veterinary and medical science was still developing, it looks at things such as Disease, Zodiac, & Bloodletting Charts.
An important ingredient to medieval and Renaissance human healing was Astrology, whereby the influence of the stars on the body was studied and carefully charted. Veterinarians did the same with horses. In these two charts, the signs of the zodiac are associated with different parts of the body: for example, don’t treat the head while Aries is in the sky.
Of course, ideas that were implausible, unsupported by evidence or which just failed were eventually abandoned. These people didn't simply believe in nonsensical things: they were attempting to systematise medical knowledge and understand disease processes. It is through them that we have our current knowledge (which, in itself, is still developing and certainly not complete).
Nonetheless, there are others today who still, in the face of evidence and knowledge, still practice arcane arts in the treatment of horses, such as pricking undetectable, unseen meridians, manipulating invisible, untouchable "energies", gazing into the horse's eye to diagnose, and a plethora of other "traditional" (but discarded) methods.
Such people would do well to consider the Zodiac Horse of Filippo Scaccho da Tagliacozzo and the Zodiac Horse of Martín Arredondo. The astrologically affected areas are different in each case. Though it is traditional, and it has been around for hundreds of years. Which does not make it proven.