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.