The breeders implemented rigorous endurance tests to help evaluate horses for breeding. In these events known as "La Marcha", the horses are ridden over a 750 km (466 mi) course to be completed in a 75 hours split in 14 days. No supplemental feed is allowed. The horses are required to carry heavy loads of 245 lb (110 kg) on their backs and may only eat the grass at the side of the road. At the end of the day, a veterinarian checks the horses.