Yearlings will most likely be fully weaned and independent of their mothers. They will be sleeping less and spend more of their resting time standing rather than lying down. Youngsters are very curious and enjoy mouthing anything they can find in their pastures or stalls. Play balls and other safe toys can satisfy their curiosity. Youngsters will play amongst themselves, play fighting, galloping and bucking.
Care is needed to keep colts separated from mares in heat. Some colts start showing an interest in mares at a very young age and some particularly precocious individuals may be able to breed a mare.
Although a colt is not technically reproductively mature until it is about 2-3 years old many a breeding accident has happened with a colt thought too young to be fertile. Gelding (castration) can be done as soon as the testes have descended into the scrotum.
If the prime reason for a horse's existence is as a pleasure horse than the sooner gelding is done the better. Although some breeders may have reasons to geld later, for the average horse owner a young gelding may be much easier to deal with than a young stallion who is more interested in mares than paying mind to its handler.
During this time the young horse should continue learning to be obedient, to lead quietly, stand tied for grooming, vet and farrier. Very short training sessions on the lunge line or in the round pen can begin. It is important that a young horse not be overworked to protect the joints in its legs and back. As the horse approaches its second year, it may learn to carry a bit and saddle. But a horse under the age of two should not carry any weight.