What should I know about horse blankets and when should they be used?

Horse blankets serve several distinct purposes — waterproofing during rain, insulation during cold weather, protection from flies during warm weather, and cooling sheet use after exercise — and understanding which purpose a specific blanket is designed for helps a horse owner avoid both under-blanketing horses that need warmth and over-blanketing horses that regulate their own temperature effectively. The decision of whether to blanket a horse at all is more nuanced than many horse owners realize. Horses have a remarkable ability to thermoregulate through their coat, their movement, and their dietary caloric conversion. The horses that genuinely benefit most from winter blanketing are those that have been body clipped, older horses with reduced thermoregulatory efficiency, horses that have been conditioned in warm climates and are not acclimated to cold, and horses that are thin or in poor body condition. Blanket fit affects both the horse's comfort and the blanket's function. A blanket that is too small pulls forward on the shoulders and restricts movement; one that is too large slides back and bunches, creating pressure sores and potentially tangling the horse's legs in loose fabric. The blanket should lie flat across the back without pulling, allow free shoulder movement, and stay in position through normal movement. Waterproof blankets protect horses from rain and wind but must be breathable to prevent moisture accumulation from sweat and body heat beneath the blanket. A waterproof but non-breathable blanket creates a humid environment under the blanket that can cause skin problems and chilling when the horse's sweat cannot evaporate.