A study of correlation of closure of the distal radial physis with performance and injury in the Standardbred.

The distal radial physes of 113 two-year-old Standardbreds were radiographed an average of 2.6 times each during an average of 4.72 +/- 1.7 months, beginning May 1, 1975. The radiograph of each physis was graded C, B-, B, B+, or A (closed), and the date of closure was determined by a method that proved to be reliable. The average age of closure of the distal radial physes was 29.8 +/- 1.6 months, with age of closure ranging from 26 to 35 months. There were no statistical differences between age of physeal closure of colts, geldings, or fillies; pacers or trotters; "well-bred" or other horses, or between horses by the same sires or from mares by the same sires. Most of the 2-year-old racing was done before physeal closure, the average date of closure being approximately Sept 25, 1975. The average birth date of the horses was March 30, 1973. Eighty of the horses raced an average of 10.5 times, and 46 of them won an average of 2.6 races. There was progressive increase of the number of horses in the more mature classifications (B-, B, B+, to A) as they; first raced, won their first race, went their fastest mile, won their fastest mile, and attained more spped. There was no correlation between age or month of closure of the physes and money won, races won, fastest mile, or fastest win mile during the 2-year-old year. Of the 113 horses, 62 (55%) had injuries--19 major and 57 minor injuries. A significant relationship was not found between physeal classification and the incidence of injury. The number of injuries was also found not to be related to the number of races, number of races won, money won, or to the fastest mile. There was a weak indication that horses with physes classified as C or B- (very immature) may not have raced quite as well as the more mature horses and may have had a slightly higher incidence of injury.