Closure of the distal radial epiphysis and its relationship to unsoundness in two year old thoroughbreds.

Abstract: The careers of many Thoroughbred racehorses are marred or terminated prematurely by unsoundness which develop when racing as two year olds. Common problems are sore-shins, carpitis, splints, sesamoiditis, sesamoid fractures and sprained joints and tendons. There appears to be no recorded information on the incidence of these conditions or of overall wastage in two year old Thoroughbreds but the results of personal observations and communications with practising veterinarians suggest that the incidence of unsoundnesses and relate these to skeletal maturity Australia. This is probably due to an increased emphasis on the racing of two year olds because many owners desire to give their horses an early opportunity to become profitable. In Australia many Thoroughbreds are actually racing before their second birthday at which age they are relatively immature and much of the unsoundness which develops can in general terms be attributed to immaturity, overwork, or defective conformation, or a combination of these factors. Although many of the conditions commonly encountered are amenable to medical or surgical treatment, results are difficult to assess especially in terms of regaining full potential. Much effort, time and money is wasted and the prevention of unsoundness, if it is possible, would be eminently more satisfactory. For these reasons the authors set out to study the progress of a group of two year old Thoroughbreds, to record the incidence of the various unsoundnesses and relate these to skeletal maturity as measured by radiographic closure of the distal radial epiphysis at the commencement of their racing careers. Work on similar lines has been in progress in the USA for some time. Studying the distal epiphysis of the third metacarpal bone, Monfort (1967) recorded a higher incidence of lameness and poorer performance records in horses in which this epiphysis closed either early (7 months) or late (12 months +). Studying the epiphysis of the tuber calcis, Banks et d (1969) gained the impression that there was a reduced incidence of lameness if horses were withheld from training until this epiphysis had closed. Other workers (Reed 1965) have used the distal radial epiphysis as an indicator of maturity, but a critical evaluation of the practice has not been recorded.