Surprisingly, horses having their first race during their 2-year-old season had longer racing careers than horses first racing at three years or older. The reasons for this difference could not be determined. However, it is likely that many of the horses not raced until they were three years old or older did enter training as 2-year-olds, and injury (or possibly a lack of athletic ability) might have delayed their racing debut. These factors could contribute to a shorter racing career. Bailey and his colleagues also examined injury rates in a group of 169 2- and 3-year-old racehorses. The most common injury in 2-year-olds was shin soreness, which was present in 42% of 160 horses that began training as 2-year-olds. Many of those horses developed shin soreness a second or third time as 2- or 3-year-olds. In 3-year-olds, knee problems were the most common cause of lameness, while fetlock injuries were present in both age groups. Injuries to tendons and ligaments were much less common, as were very serious breakdown injuries. Overall, days lost to training because of injury or illness were higher in 2-year-olds (3.1%) than in 3-year-olds (2.2%), probably reflecting the greater impact of shin soreness in the younger horses.
The economics of Thoroughbred racing are such that most owners and trainers aim to have their horses ready for racing as 2-year-olds. On the other hand, we know that lameness problems are the most important reason for wastage in Thoroughbred racehorses, and some perceive that these injuries are due, in large part, to the training and racing of horses too early in life. Is this fact or fiction? The short answer is that we don't know, writes Dr. Ray Geor in the January edition of The Horse. However, recent epidemiological studies by Craig Bailey and his colleagues from the University of Sydney aimed to shed further light on causes of wastage, at least under Australian training and racing conditions. As in the United States, considerable emphasis is placed on 2-year-old racing in Australia. In one project, researchers studied the racing careers of 553 Thoroughbreds catalogued for a yearling sale in 1991. Of the 553 horses, 279 (50.5%) had their first start as 2-year-olds, 162 (29.3%) as 3-year-olds, and 20 (3.7%) as 4- or 5-year-olds. Eighty-one horses (14.6%) did not make it to the races, while the remaining 11 horses were lost to follow-up.