Summary Reasons for performing study: Radiography in presale examinations of TB yearlings has become standard practice in recent years. Objectives: To describe the prevalence and distribution of radiographic changes in the fetlocks, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings in central Kentucky when these joints were examined as part of routine pre‐ and post sale evaluations. Methods: Horses subjected to radiographs included the fore (n = 1127) and hind (n = 1102) fetlocks, carpi (n = 1130), tarsi (n = 1101), stifles (n = 660) and fore feet (n = 300). Radiographic changes were categorised by location and type of change present (e.g. lucency, fragment) for each series. Results: In the fore fetlocks 1.6% had fragmentation of the proximal dorsal first phalanx and 0.5% fragmentation of the proximal palmar aspect. In the hind fetlocks 5.9% had fragmentation at the plantar aspect and 3.3% fragmentation dorsally. Lucencies, fragments or loose bodies were detected at the dorsal aspect of the distal third metacarpus in 2.8% and, at the same location on the third metatarsus, 3.2%. Most yearlings (98%) had vascular channels in the proximal sesamoid bones and irregularvascular channels (>2 mm wide or with nonparallel sides) were more common (79%) than regular vascular channels (56%). The intermediate ridge of the distal tibia was the most common location for fragmentation in the tarsus (4.4%). Conclusions: While some radiographic changes, e.g. vascular channels in proximal sesamoid bones, are very common in Thoroughbred yearlings, others, e.g. fragmentation or subchondral lucency within joints are quite rare usually affecting less than 5% of the population. Potential relevance: Veterinarians should expect to find radiographic changes in Thoroughbreds presented for examination prior to the yearling sales. The rarity of some changes thought to affect soundness or racing performance will make further invesigation of these conditions in horses without clinical signs more difficult.

Summary Reasons for performing study: Although the radiographic examination of yearlings has become commonplace at some large Thoroughbred sales, there are few data to support the decisions facing veterinarians who are asked to evaluate future racing potential. Objectives: To identify radiographic changes in the fetlocks, proximal sesamoid bones, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings associated with future racing performance during ages 2 and 3 years. Methods: Radiographs from routine pre‐ and post sale examinations of 1162 yearlings were used to identify individual radiographic changes in sale yearlings. Starting a race, the percent of starts placed, money earned and earnings per start were used to assess racing performance and examined for associations with the radiographic changes observed. Results: Overall 946 (81%) yearlings started at least one race during ages 2 or 3 years. Fourteen of 24 (58%) yearlings with moderate or extreme palmar supracondylar lysis of the third metacarpus, 8 of 14 (57%) of those with enthesophyte formation on the proximal sesamoid bones and 19 of 30 (63%) of those with dorsal medial intercarpal joint disease started a race. The oDs of starting a race when age 2 or 3 years were 3 times lower for yearlings with these changes (P<0.01) compared with yearlings that did not have these changes. Twenty‐five of 36 (69%) yearlings with proximal dorsal fragmentation of the first phalanx in the hind fetlock started a race and these yearlings were also less likely (OR = 0.51, P = 0.07) to start a race. Yearlings with enthesophyte formation on hind proximal sesamoid bones placed in a smaller percentage of starts (16%, P = 0.01) earned less money ($987 US, P = 0.02) and had lower earnings per start ($252 U S, P = 0.03) compared to starters without this change. Conclusions: Although many of the changes observed on radiographs of sale yearlings do not appear to influence future racing performance, some are associated with reduced performance. Potential relevance: The results of this study are best applied in parallel with the clinical impressions of veterinarians experienced in examining radiographs of sale yearlings. Some findings support those established in the literature as incidental findings and others suggest new areas for concern not previously reported as a problem in Thoroughbred sale yearlings.

The objective of this study was to determine if damage to the articular cartilage alone or articular cartilage plus subchondral bone of the distal medial femoral condyle of young, exercised horses resulted in the formation of subchondral cystic lesions. Twelve Quarter Horses (age 1-2 years), free of clinical and radiographic signs of osteochondrosis and lameness were used. In 6 horses (Group 1), a 15 times 1 mm linear full thickness defect in the articular cartilage was made arthroscopically on the weightbearing surface of the distal aspect of the medial femoral condyle. In the other 6 horses (Group 2), a 15 times 3 mm full thickness elliptical cartilage defect was made, followed by burring a 5 mm diameter, 4 mm deep hole into the subchondral bone. Three weeks after surgery, all horses were hand walked and trotted for 2 weeks and then exercised for 6 min daily, 5 days a week for the next 14 weeks on a treadmill. They were then turned onto a small paddock for 6 weeks (6 months total). The development of subchondral cystic lesions was determined using radiography. Bone activity in the femoral condyle was monitored with nuclear scintigraphy. All horses that developed subchondral cystic lesions radiographically were subjected to euthanasia for gross and histological examination of the lesions. No subchondral cystic lesions and no clinical abnormalities were detected in the horses in Group 1. Subchondral cystic lesions developed radiographically in 5 of 6 horses in (Group 2). Scintigraphic findings of horses with subchondral cystic lesions were inconsistent. Histological examination of lesions revealed variable quantities of fibrous connective tissue, fibrocartilage and bone, with evidence of bone remodelling adjacent to the subchondral cystic lesion. The results suggest that damage to articular cartilage plus subchondral bone, but not articular cartilage alone, of the distal medial femoral condyle may lead to the development of subchondral cystic lesions. These findings indicate that all subchondral cystic lesions in horses may not be osteochondrosis-type lesions and that trauma to weightbearing articular surfaces of young horses may be a predisposing factor.

Abstract. Beginning in summer 1977 and continuing through four consecutive seasons, we examined lame limb joints from 106 partially fattened cattle and 28,235 pairs of occipital condyles from fully fattened cattle for osteochondrosis. Of the 106 lame cattle, nine (8.5%) had characteristic lesions, usually in their stifle joints, and of the 28,235 atlanto-occipital joints, 1063 (3.8%) had lesions on their condyles.Slices of affected articular cartilage and subjacent bone were studied radiographically and histologically. Radiographs showed subchondral defects and epiphyseal "cyst-like" lesions, and histologic sections showed disarrayed and degenerated chondrocytes. Splits occurred along osteochondral junctions or in adjacent cartilage or bone. Some bone trabeculae had been replaced by fibrous tissue that, in some areas, extended deep into epiphyses.Osteochondrosis, a degenerative change in articular and growth plate cartilage of rapidly growing animals, is characterized clinically by prolonged limb lameness, and anatomically by disarray of chondrocytes, inadequate provisional calcification of cartilage, failure of endochondral ossification, retention of cartilage, and splits in cartilage and bone [3].Beginning in summer 1977 and continuing through four consecutive seasons, we examined small samples of limb joints and large samples of atlanto-occipital joints from slaughtered cattle for arthropathies and found this disease. Materials and MethodsMost cattle were Hereford, Angus, Charolais, and their crosses. Steers predominated. Their ages at slaughter ranged from 15 to 18 months. All had been fed high concentrate rations in feedlots of eastern Colorado, western Nebraska or western Kansas. They were slaughtered at one of three companies under federal inspection. Cattle with osteochondrosis were of two categories: those with limb joint lesions and lameness, and those with atlanto-occipital joint lesions and no recognized clinical signs. Some had become lame during the fattening period and were slaughtered prematurely for recovery of value. All others had been fattened through 90 to 140 days.During each of the four seasons, a sample of at least 25 lame cattle and a sample of nearly 529