Does my horse need more hay?
Start with the horse, the forage and the conditions—not a one-size-fits-all number.
Quick answer
University of Minnesota Extension advises that mature horses commonly receive about 1.5–2.5% of body weight in forage, while the actual amount depends on the horse and forage quality. For a 1,000-lb horse, 2% is about 20 lb of forage per day.
Pasture counts as forage, so “how much hay?” depends on how much usable pasture the horse is actually eating.
Cold can change the requirement
Below a horse's lower critical temperature, maintaining body heat takes additional energy. Extension guidance recommends meeting additional cold-weather energy needs with forage when practical because fiber fermentation produces heat.
Wet coat, wind, limited shelter, age, acclimation and body condition can change cold tolerance, so temperature alone is not enough.
Look at the trend
Regularly check body weight and body condition. If condition is falling, don't assume cold is the only cause; determine why the horse is losing condition and involve a veterinarian or equine nutrition professional when appropriate.
Connect it to tonight's weather
Should I Blanket can tell you when cold, wind and rain are becoming relevant. Use that alongside the horse's condition and feeding plan.
Sources
University of Minnesota Extension: Feeding the mature horse
University of Minnesota Extension: Caring for your horse in winter
University of Minnesota Extension: Using hay in horse diets
Educational information only. Individual feeding plans should account for health, workload, forage analysis and veterinary/nutrition guidance.