Weanlings are not capable of reproduction. Puberty occurs in most horses during their yearling year. Therefore, some young horses are capable of reproduction prior to full physical maturity, though it is not common. Two-year-olds sometimes are deliberately bred, though doing so, particularly with fillies, puts undesirable stress on their still-growing bodies. As a general rule, breeding young horses prior to the age of three is considered undesirable. Early training In spite of rapid growth, a foal is too young to be ridden or driven. However, foals usually receive very basic horse training in the form of being taught to accept being led by humans, called halter-breaking. They may also learn to accept horse grooming, hoof trimming by a farrier, having hair trimmed with electric clippers, and to become familiar with things it will have to do throughout life, such as loading into a horse trailer or wearing a horse blanket. Horses in general have excellent memories, so a foal must not be taught anything as a young horse that would be undesirable for it to do as a full-grown animal. In either case, foals that have not bonded to their mothers will have difficulty in pasture. The mare will find it more difficult to teach the foal to follow her. Other horses can have difficulty communicating with the foal and may ostracise it due to speaking a different "language". It can be difficult to lead a foal that has never even been led by its dam. Horses are not fully mature until the age of four or five, but most are started as working animals much younger, though care must be taken not to over-stress the "soft" bones of younger animals. Yearlings are generally too young to be ridden at all, though many race horses are put under saddle as "long" yearlings, in autumn. Physiologically young horses are still not truly mature as two-year-olds, though some breeders and most race horse trainers do start young horses in a cart or under saddle at that age. The most common age for young horses to begin training under saddle is the age of three. A few breeds and disciplines wait until the animal is four. See also Deciduous hoof capsule References Further reading Lyons, John and Jennifer J. Denison. Bringing Up Baby. Primedia Enthusiast Publications, 2002. . Describes methods of training a young horse from birth until it is old enough to