Give a stream of consciousness and then the final answer. The withers is the ridge between the shoulder blades of an animal, typically a quadruped. In many species it is the tallest point of the body, and in horses and dogs it is the standard place to measure the animal's height (in contrast, cattle are normally measured to the top of the hips).

Answer this question: where are the withers located on a horse?
The relevant information is: The withers is the ridge between the shoulder blades of an animal, typically a quadruped.
So, the final answer is between the shoulder blades.