Development of osteochondrosis in the tarsocrural joint and osteochondral fragments in the fetlock joints of Standardbred trotters. II. Body measurements and clinical findings

In a stud survey, 77 Standardbred foals (35 colts, 42 fillies) were examined 6 times from birth to the age of 16 months. In addition to the radiographic examination of the tarsocrural and fetlock joint areas, the horses were measured for height at the withers and at the croup, the circumference of the girth, carpus and cannon, and the length of cannon, and their conformation assessed according to a standardised protocol. The examination was completed by clinical examination, including thorough palpation of the extremities. All examinations were done by the same person. The foals were weighed each month. The metric observations were precorrected according to a model including the effects of sex, year of birth and the regression on individual recording age. Eight foals (4 colts, 4 fillies) that developed radiographic signs of tarsocrural joint osteochondrosis (OC) had a higher body weight at birth (54.0 kg vs 51.0 kg) and continued to be heavier and have a significantly higher average daily weight gain than did unaffected foals (12 months 337.8 kg vs 316.8 kg, 0.80 kg/day vs 0.74 kg/day). They also had a larger frame than did horses without tarsocrural OC, including a greater height at the withers and at the croup, and had a markedly larger circumference of the carpus and cannon.From 5 months of age onwards, there was a significantly higher incidence and more severe degree of synovial effusion in the hock joint in horses with OC. Enlargement of the distal physeal region of the metacarpus was more common and more pronounced between 3 and 8 months of age in horses with tarsocrural joint OC. Eleven foals (3 colts, 8 fillies) with fetlock findings, palmar/plantar osteochondral fragments (POF) and/or ununited palmar/plantar eminences (UPE), were slightly lighter (birth weight 50.8 kg vs 52.0 kg, 12 months 316.3 kg vs 321.6 kg). The average daily weight gain, as well as the different body measurements, were similar in affected and in unaffected horses. There was no relation between radiological findings of POF or UPE and the degree of synovial effusion or other clinical signs in the fetlock area, including the distal physeal region. The early radiological signs of OC and the observed difference in body size at birth indicate that the pregnancy period and the first months in the foal's life are of major importance for the development of OC. The differences in body weights, body measurements and clinical signs between horses affected by tarsocrural OC and fetlock POF or UPE are indications that the pathogenesis of these lesions differs