What Cold Weather Does Inside The Horse
Cold air causes muscles to tighten and blood vessels near the surface to constrict. The body tries to protect vital organs and conserve heat. As a result, muscles and connective tissue feel less elastic until movement warms everything back up.
Stalls, smaller winter paddocks, and risk of ice can also mean less free movement. Less motion plus cold muscles is a recipe for stiffness, especially in older horses or those with a history of hard work.