The influence of birth weight, rate of weight gain and final achieved height and sex on the development of osteochondrotic lesions in a population of genetically predisposed Warmblood foals.

The influence of inherent variables (sex, birth weight, final achieved height, monthly weight gain rates and osteochondrosis (OC) status of the parents) on the occurrence of osteochondrotic lesions in the femoropatellar and tarsocrural joints in a group of foals was investigated as part of a research project aimed at the study of the development of osteochondrosis and the influence of exercise on the development of the musculoskeletal system in Warmbloods. The foals were genetically predisposed to develop OC, being offspring of sires that all had radiographically proven OC in either the femoropatellar or the tarsocrural joint. In the mare population the incidence of femoropatellar OC was 16% and of OC in the tarsocrural joint 7%. Foals (n = 43) were weighed at birth, and thence every second week until euthanasia at 5 (n = 24) or 11 (n = 19) months. Height at the withers was taken twice, at birth and at euthanasia. Weight gain rates were calculated for months 1, 2, 3, 4, 5, 7, 9 and 11 and for the entire 5 or 11 month period. Osteochondrosis status of the parents in the 2 joints with respect to the distal tibial sagittal and lateral femoral trochlear ridges was determined radiographically. In all foals, radiographs were taken from the same sites prior to euthanasia. After euthanasia the joints were examined macroscopically and histologically for the presence of osteochondrotic lesions and classified as OC positive (OC+) or negative (OC-). No influence of sex on the prevalence of OC in either of the joints could be established. Also, no relationship between the prevalence of tarsocrural OC and any of the growth variables was found. Foals positive for femoropatellar OC had a significantly higher weight gain rate in the third and fifth month. Animals killed at 11 months that were OC+ in the femoropatellar joint had a significantly higher weight gain rate over the 11 month period, weighed more at 11 months, and were taller at the withers and at the croup than non affected animals. Offspring of tarsocrural OC- parents did not have a lower number of lesions in this joint than foals of which at least one of the parents was affected, but no foals that were offspring of femoropatellar OC- parents themselves showed lesions. It was concluded that, in this selected group, sex had no influence on the occurrence of OC lesions. Even in this relatively homogenous group weight gain rate affected the occurrence of lesions in the femoropatellar joint, but not in the tarsocrural joint. This corresponds with the different time-frames in which the lesions develop in the various joints and with the existence of windows of 'susceptibility'.