Be best to get a few books on horses and horse care in the Middle Ages, I am sure they are out there, identify the time frame you are looking at for your writing, and then see what may be on Amazon for a few pennies, if you are lucky.
The terms we use now, are vastly different from what was used in earlier times, as well as some things that were common back then, may no longer be a term used.
Better to do deeper research. One place you might also look to, is the SCA, as they are fairly accurate from the ones I have known, on their dress and mannerisms, so it stands to reason they would have knowledge to share.
Horses make me a better person.