Horses that spend the winter on dry lots eating hay have to be carefully managed once spring grass starts to sprout. Horses have delicate digestive systems, and any abrupt change in feed is liable to cause colic or founder. In fact, the United States Department of Agriculture notes that 54 percent of all laminitis cases are due to poor pasture management.
To prepare your horses, especially overweight horses, draft horses and ponies who are at much higher risk for founder, start slowly. Hand-graze horses for 15 to 20 minutes each day to begin with, gradually increasing their time on pasture over a period of weeks. Keep an eye on your horses by checking for heat in their hooves, elevated/bounding digital pulses or "parking"-where the horse's hind legs are far out behind him-and if you notice any of these signs call your veterinarian immediately.