Most healthy adult horses with full winter coats do not need blankets until temperatures drop below 20F (-7C). Over-blanketing prevents normal coat loft and causes horses to sweat, which is worse than being cold. The decision to blanket should be based on body condition score, coat status, and weather -- not the human's feeling cold.
| Situation | Blanket Needed | Why |
|---|---|---|
| Full coat; BCS 4–5; shelter; above 20°F | None | Coat loft provides adequate insulation — blanketing prevents normal loft |
| Body-clipped; shelter; 20–40°F | Lightweight turnout (100–200g) | Coat removed; insulation must be replaced |
| Thin horse or elderly (20+); 20–40°F | Mediumweight (200–300g) | Reduced thermoregulation capacity |
| Rain + wind; any temp; clipped horse | Waterproof turnout at appropriate weight | Wet horse loses heat 3–4x faster than dry |
How Horses Thermoregulate
Horses are large animals with a low surface-area-to-volume ratio and efficient circulatory thermoregulation. Their winter coats trap air between the hairs via a piloerection reflex, creating insulation that can maintain body temperature in temperatures well below freezing. A horse with a full winter coat, adequate body condition score (4-5 on the 1-9 Henneke scale), shelter from wind and precipitation, and adequate forage has excellent cold tolerance. Shivering (a sign the horse is working to stay warm) is an early indicator that conditions have exceeded thermoregulation capacity.
When Horses Need Blankets
Blanket when: the horse is body-clipped (clipping removes the insulating coat); the horse is a thin keeper or has a body condition score below 4; the horse is elderly (20+) with reduced thermoregulation; the horse is sick, recovering from surgery, or immunocompromised; temperatures drop below 20F with wind chill; rain and wind combine (a wet, windy horse loses heat 3-4x faster than a dry horse); the horse does not have access to shelter. Young horses under 6 months may also need blanketing in severe cold before their thermoregulation is fully developed.
Blanket Weights and Selection
Blankets are rated by fill weight (grams of insulation) and waterproofness (denier). No-fill turnout sheets (0g fill): wind and rain protection only, used in temperatures 40-50F for clipped horses or rain protection. Lightweight turnout (100-200g): 20-40F range for average horses. Mediumweight (200-300g): 10-20F. Heavyweight (300-400g): below 10F. For stalled horses without rain exposure, stable blankets (not waterproofed) with similar fill ratings work. Measure horses from center of chest to tail base along the side for correct sizing -- a blanket that slides back puts pressure on the withers.
Blanket Management
Check under blankets daily -- if the horse is sweating, the blanket is too heavy or temperature has risen. Horses can develop pressure sores and rubs at the withers, shoulders, and chest with poorly fitted or wet blankets. Dry blankets after rain before re-use -- a soaking wet blanket provides no insulation and actively chills. Rotate to a second blanket if the primary needs drying. Check surcingles and leg straps for proper adjustment (2-3 finger width gap at belly, leg straps crossed but not tight).
The Over-Blanketing Problem
Over-blanketed horses sweat, which dampens the coat and eliminates its insulating capacity. Damp horses in cold conditions chill rapidly when blankets are removed for exercise or when the temperature fluctuates. Horses maintained in overly warm conditions also fail to develop adequate winter coat, becoming dependent on blankets for conditions they would normally handle unassisted. Assess each animal individually rather than blanketing all horses on the same schedule.
Sources: Henneke DR et al., Relationship between body condition score and body fat in mares, Equine Veterinary Journal 1983; NRC Nutrient Requirements of Horses; AAEP equine care guidelines; University of Minnesota Extension horse management resources; Cymbaluk NF, Christison GI, Environmental effects on thermoregulation in horses, Journal of Animal Science 1990.