Radiographic changes in Thoroughbred yearlings. Part 1: Prevalence at the time of the yearling sales

Computed Tomographic Evaluation of the Sagittal Ridge of the Third Metacarpal Bone in Young Thoroughbred Racehorses: A Longitudinal Study

Metacarpophalangeal joint region pain is a common cause of lameness in racehorses. Radiological abnormalities in the sagittal ridge (SR) of the third metacarpal bone have been associated with joint effusion, lameness and reduced sales prices. The aims were to describe computed tomographic (CT) appearance of the SR in racehorses, and to document the progression of these findings over three assessments. Forty yearlings were enrolled at the first examination (time 0). Re-examinations were performed twice, approximately six months apart on 31 (time 1) and 23 (time 2) horses, respectively. Computed tomographic examinations of both metacarpophalangeal regions were performed with the horses in a standing position. Computed tomographic reconstructions were analysed subjectively and objectively. The mean Hounsfield Unit values (Hus) of eight radial segments and location, size and shape of hypoattenuating lesions were recorded. Mean Hus at time 1 were higher than at time 0. There was no difference between mean HU at times 1 and 2. The mean HU values of the dorsal half were higher in the right forelimbs and in fillies. Hypoattenuation was identified in 33/80 (41.3%) limbs at time 0, in 22/62 (35.5%) limbs at time 1 and in 14/46 (30.4%) limbs at time 2. All hypoattenuations were located in the dorsodistal aspect of the SR. The most common shapes were hypoattenuating lesions elongated proximodistally and those extending towards trabecular bone. An increase in attenuation of the SR occurred in the first six months of training. Hypoattenuating lesions could decrease in size and could resolve during early training. In this population, these lesions were not associated with lameness.

Racing Performance and Sale Result in 145 Thoroughbreds after Arthroscopic Removal of Osteochondral Fragments from the Lateral Femoral Trochlear Ridge as a Yearling (2012-2015)

OBJECTIVES

 The lateral trochlear ridge (LTR) of the femur is the most common predilection site for osteochondritis dissecans (OCD) in the equine stifle. The objective was to investigate the relationship between lesion size, racing performance, and sale result of Thoroughbreds with LTR OCD following arthroscopic removal as a yearling.

METHODS

 In this retrospective study, medical records of 145 Thoroughbreds from one equine hospital that underwent surgery for LTR OCD were reviewed; the length and depth of the lesions were measured on preoperative radiographs. Horses were allocated to group S if they were presented to a public yearling sale post-surgery, and horses in group NS were not. Each horse from group S was matched with two control horses from the same sale (group C). Influence of lesion size on racing performance and sale result was analyzed. Racing performance and sale results were compared between different categories of OCD lesion sizes and between the groups.

RESULTS

 Lesion length and depth did not affect racing performance and did not differ between group S and group NS. However, group S did perform significantly better than group NS. When comparing groups S and C, there were no significant differences in racing performance and sale result.

CONCLUSION

 Thoroughbreds that had arthroscopic surgery for LTR OCD as a yearling and were presented on a public yearling sale performed comparable to Thoroughbreds that showed similar potential as a yearling. Sale result is not significantly affected in our study.

Substantial variability exists in the interpretation of survey radiographs among equine veterinarians

BACKGROUND

Radiographs are a common diagnostic tool utilised during pre-purchase examinations, yet differences surround their interpretation among equine veterinarians.

OBJECTIVES

(1) To determine veterinarians' subjective impressions of a spectrum of radiographic abnormalities regarding suitability for purchase; (2) To determine how veterinarians' years in practice, primary discipline or board certification status influence their subjective impression of radiographic abnormalities, and (3) To determine how horses' discipline, current level of work (working at intended level vs. future prospect) and buyer intent (sell vs. retain ownership) influence veterinarians' subsequent recommendation.

STUDY DESIGN

Worldwide electronic survey of veterinary professionals.

METHODS

Four radiographic series of navicular bones, tarsi, and stifles, representing varying degrees of pathological change (normal, mild, moderate and marked) were presented. Respondents (n = 211) graded their level of concern from 1 (no concern) to 10 (very concerned) based on the radiographs and case scenarios presented.

RESULTS

Overall, as the grade of pathological change increased for each anatomical location, so did the level of veterinarian concern, but a wide range of answers were submitted for all grades of pathology. Board certified practitioners had a higher level of concern over marked radiographic changes of the navicular bone for both western performance and English sport horses as well as prospect horses (mean = 7.2 vs. 6.1; P = 0.009; 95% CI for difference = [0.3, 2.0]). Board certified respondents had a lower level of concern over marked radiographic changes of the tarsus regardless of the performance status of the horse (mean = 7.1 vs. 8.0; P = 0.008; 95% CI for difference = [-1.5, -0.2]). Western performance horse practitioners had a lower level of concern over mild radiographic changes of the tarsus regardless of the performance status of the horse (mean = 3.3 vs. 4.2; P = 0.009; 95% CI for difference = [-1.6, -0.2]).

MAIN LIMITATIONS

Only one example of each pathological grade per anatomical region was presented.

CONCLUSIONS

On survey radiographs, the perceived clinical relevance of radiographic abnormalities among equine practitioners differs widely, making purchase recommendations highly variable.

Racing performance of juvenile Thoroughbreds with femoropatellar osteochondrosis at auction: A retrospective case-control study

BACKGROUND

Osteochondrosis dissecans (OCD) is common in the femoropatellar joint in Thoroughbred yearlings for sale at auction and there is no consensus on the effect on racing outcomes.

OBJECTIVES

Describe femoropatellar OCD in juvenile Thoroughbreds and compare the racing performance of affected Thoroughbred horses to siblings and unaffected horses from the same sale.

STUDY DESIGN

Retrospective case-control study of juvenile horses born 2010-2016.

METHODS

Radiographic reports from 27 Thoroughbred auctions of weanling (5-11 months of age) and yearling (12-22 months of age) horses were reviewed to identify femoropatellar OCD. Age and sex of cases and controls were obtained from the sales catalogue. Racing performance was obtained from an online database. Correlation between lesion characteristics and racing performance were assessed using Pearson and Spearman correlations for continuous and ordinal/categorical variables respectively. Racing performance was compared between cases and sibling controls and age- and sex-matched sale number controls from the same sale with Poisson distribution and log link. Significance level of alpha = 0.05 was used.

RESULTS

Femoropatellar OCD was identified in 429 horses with North American race records. OCD was present on 519 lateral trochlear ridges and 54 medial trochlear ridges. There were more males in the case group (70%) than in the sibling control group (47%). Case racing performance was compared to 1042 sibling and 757 hip controls. There were significant but small decreases in racing metrics of cases and increases in males for years raced, total starts, starts for 2-5 years of age, total placings, and placings at 2-4 years of age. Analysis of specific lesion metrics revealed weak correlations for performance outcomes (positive and negative) resulting in an inability to draw firm conclusions.

MAIN LIMITATIONS

Retrospective study where case management was unknown.

CONCLUSIONS

Femoropatellar OCD in juvenile Thoroughbreds for sale at auction decreases some racing outcomes.

Subchondral lucencies of the medial femoral condyle in yearling and 2-year-old Thoroughbred sales horses: Prevalence, progression and associations with racing performance

BACKGROUND

Subchondral lucencies (SCLs) in the distal aspect of the medial femoral condyle (MFC) of young Thoroughbred horses are a source of controversy on presale radiographs. There is limited scientific evidence regarding the risk of progression and impact on future racing performance.

OBJECTIVES

To (1) identify the prevalence of MFC SCLs on sales repository radiographs in yearling and 2-year-old Thoroughbreds; (2) identify any association between grade of MFC SCL and future racing performance and (3) monitor changes in MFC SCL grades between yearling and 2-year-old sales.

STUDY DESIGN

Prospective cohort study.

METHODS

Radiographs were obtained with consignor permission from a 2016 yearling sale and five 2017 2-year-old sales. Stifle radiographs were evaluated and MFC SCLs graded on a scale of 0-3. Axial MFC lucencies were recorded separately. Maximum MFC grades per horse were analysed for associations with racing performance outcomes, adjusted for sex, to the end of the horses' 4-year-old racing year. Analysis was via logistic, negative binomial or linear regression as appropriate, with the threshold for significance set at α = 0.05.

RESULTS

Radiographs from 2508 yearlings (5016 stifles) and 436 2-year-olds (872 stifles) were included in the study. MFC SCLs of grades 1-3 were observed in 242 (9.65%) yearlings and 49 (11.2%) 2-year-olds. Bilateral MFC SCLs of grades 1-3 were observed in 54 (2.2%) yearlings and 12 (2.8%) 2-year-olds. Grade 1 MFC SCLs in yearlings either remained unchanged (14/31), progressed to a grade 2 (6/31) or resolved (11/31) by the 2-year-old sale. Grade 2 MFC SCLs in yearlings remained unchanged (6/10), progressed to a grade 3 (2/10) or improved to a grade 1 (2/10). Yearlings with a grade 3 MFC SCL had a 78% probability of starting a race (95% confidence interval [CI] 58.2-89.6%), compared with an 84% probability of racing for grade 0 yearlings (95% CI 82.7-85.8%). Six of the seven yearlings with axial MFC lucencies raced.

MAIN LIMITATIONS

This study may underestimate the prevalence of severe lesions in the general yearling population of U.S. Thoroughbreds. However, the convenience sample used is representative of the population of interest at sales. The study design could not address exclusions prior to sale.

CONCLUSIONS

Grade 1 MFC SCLs are the most common type seen in yearling and 2-year-old sales horses. The majority of yearling grade 1 MFC SCLs resolved or remained static by 2-year-old sales. It was also possible for grade 2 and 3 MFC SCLs to improve one grade between sales. Fewer sales yearlings with a grade 3 MFC SCL raced, but in those that did race there was no evidence of worse performance compared to unaffected peers. Axial MFC lucencies did not affect racing performance.

Magnetic Resonance Imaging, Computed Tomographic and Radiographic Findings in the Metacarpophalangeal Joints of 40 Non-Lame Thoroughbred Yearlings

Most catastrophic injuries in Thoroughbred racehorses involve the fetlock. There is no description of comparative imaging in Thoroughbreds entering racehorse training. The aim was to describe MRI, CT and radiographic findings in the metacarpophalangeal joint of non-lame Thoroughbred yearlings. Forty Thoroughbreds underwent low-field MRI, fan-beam CT and radiographic examinations of both metacarpophalangeal joints. Images were assessed subjectively. A hypoattenuating lesion of the sagittal ridge of the third metacarpal bone (McIII) was identified in 33/80 limbs in CT reconstructions. Cone-shaped mineralisation in the sagittal ridge was detected in MR images (n = 17) and in CT images (n = 5). Mild hyperattenuation was common in trabecular bone in the dorsomedial (36/80) and palmarolateral (25/80) metacarpal condyles in CT reconstructions. A focal lesion in the subchondral bone was seen in the proximal phalanx (n = 19) and in McIII (n = 11). Enlarged vascular channels were detected in the metacarpal condyles in 57/80 limbs and in the proximal sesamoid bones in all limbs. Signs of bone modelling are seen in yearling Thoroughbred fetlocks. Sagittal ridge lesions were common and are likely associated with osteochondrosis or other developmental osteochondral defects. Focal lesions in the subchondral bone of McIII and proximal phalanx can indicate developmental abnormalities or subtle subchondral bone injuries.

Arthroscopic removal of osteochondral fragments located within the condylar fossa of the third metacarpus/metatarsus in Thoroughbred yearlings

OBJECTIVE

To describe an arthroscopic technique for the removal of osteochondral fragments located within the condylar fossa of the third metacarpal/tarsal bone.

STUDY DESIGN

Retrospective study.

ANIMALS

Thoroughbred yearlings (n = 11).

METHODS

Osteochondral fragments located within the condylar fossa of the third metacarpal/tarsal bone identified during presale radiographic examination were removed via arthroscopy, assisted with ultrasonography in select cases. Complete fragment removal was confirmed by intraoperative radiography.

RESULTS

Fragments were successfully removed using rongeurs following dissection of soft tissue attachments using a bipolar radiofrequency probe. No postoperative complications occurred.

CONCLUSIONS

An ipsilateral arthroscopic and instrument portal coupled with ultrasound assistance and a radiofrequency probe allowed for successful removal of fragments located within the condylar fossa of the third metacarpal/tarsal bone. The technique allowed for the removal of the unstable osteochondral fragment and associated physical debris.

CLINICAL SIGNIFICANCE

The described surgical technique enables the removal of osteochondral fragments located within the condylar fossa of the third metacarpal/tarsal bone with minimal disruption to the surrounding soft tissues.

Radiographic Description of a Bone Exostosis Lesion on the Caudal Aspect of the Proximal Tibia in Three Thoroughbred Yearlings (2014-2019)

This manuscript describes exostosis lesions originating from the caudal aspect of the proximal tibia identified in three Thoroughbred yearlings as part of the routine review of presale radiographic images. These lesions are hypothesized to be osteochondromas. The identification of bony exostoses on the proximal tibia has not been reported before in current literature. As they have not been described, the future effect on performance or soundness is unknown. Although these cases were not lame at the time of detection, the future growth of the lesion and its impact on surrounding soft tissues is unknown.

Prevalence of Radiographic Signs of Osteoarthritis in Lusitano Purebred Horses

Radiographic prevalence and correlation of radiographic findings has not been performed in Lusitano Purebred horses. The aim of this study was to (1) evaluate the prevalence of primary osteoarthritis radiographic findings in Lusitano Purebred horses; (2) to assess correlations between radiographic findings in different joints of the same limb and different limbs; and (3) elucidate the effect of age in the radiographic findings. A radiographic protocol of the stifle, tarsi, fetlocks and distal limbs was done in 98 Lusitanos and the classification of the radiographs was performed using a 0-4 scale developed and applied blindly by three veterinarians. The distal interphalangeal, proximal interphalangeal, metacarpophalangeal, metatarsophalangeal, tarsometatarsal, distal intertarsal, proximal intertarsal/, tibiotarsal and femorotibial-patellar joints were evaluated. Most joints presented no abnormal findings or minor abnormal radiographic findings (82.86% grade ≤1). The most affected joint was tarsometatarsal and more severe lesions were found in tarsometatarsal and distal intertarsal. Femorotibial-patellar radiographic changes were rare (2.13%). A strong/moderate correlation was found between contralateral joints with exception hindlimb fetlocks. A moderate correlation was found between fore and hindlimbs for distal limb joints. When analyzing ipsilateral as well as diagonal distal limbs, a strong/moderate correlation was also found. The total score progressed in 0.2 score points per each year of age, revealing that age can be a statistically significant predictor for radiographic changes. Overall, Lusitano horses presented a low prevalence of severe radiographic sings of primary osteoarthritis. Findings in contralateral joints tend to be correlated.

Growth Rates of Thoroughbred Foals and In Vitro Gut Health Parameters When Fed a Cereal or an All-Fiber Creep Feed

Traditions and the economic advantage when producing big athletic Thoroughbred (TB) yearlings for sale encourage owners to feed high levels of cereals. Such diets can predispose gastric ulceration and developmental orthopedic diseases, impacting negatively on future careers. This study aimed to (1) determine if an all-fiber creep feed (total mixed fiber ration [TMFR] would sustain equal growth rates in TB foals versus a cereal-based stud cube (SC) and (2) compare pH and lactate produced by SC and TMFR in in vitro foregut and hindgut conditions. Eight TB foals in matched-pairs were fed SC or TMFR for 18 weeks. Weight gain (average daily gain [ADG]), height at wither and hip, heart girth, and body length were recorded weekly. Similar growth rates were recorded for all measurements. The ADG of TMFR and SC were 1 and 1.1 kg per head per day, respectively. In vitro foregut incubation of SC and TMFR at 37°C in pepsin HCl solution for 6 hours produced higher pH 5.84 (TMFR) compared with 5.33 (SC) (P < .05). Gas production measured fermentation rate, acidity, and lactate from TMFR and SC, incubated with fecal inoculum from the foals on the same diet. Fermentation rates and lag times were equal for both feeds; total gas produced at t50 and y50 were greater (P < .05) for SC. Lactate and pH levels were lower and higher, respectively, for the TMFR. This study showed that similar growth in TB foals was achieved on the TMFR feed and that potentially better gut health, denoted by higher pH and lower lactate levels, could be maintained by fiber compared with cereal feed.

Prevalence of Juvenile Osteochondral Conditions in Yearling Thoroughbred Racehorses in Southern Brazil

This study aimed to investigate the prevalence of juvenile osteochondral conditions (JOCCs) in yearling Thoroughbred (TB) racehorses in Southern Brazil, as well as to examine the same animals studied as weanlings by Bastos et al. (2017) and compare the radiographic findings for the two ages. Radiographs of 76 male and female TB yearlings from Paraná State, Southern Brazil, were investigated. The proximal interphalangeal, metacarpophalangeal/metatarsophalangeal (MC/MT), tarsal, and femorotibial (FT) joints were evaluated using 24 radiographic projections. The evaluation consisted of a severity index (rated as 0, 1, 2, 4, or 8), the sum of which resulted in an osteoarticular status (OAS) of good, intermediate, or poor for each animal. Radiographs of 92% of the investigated animals presented at least one finding consistent with JOCCs. The most affected region was the tarsal joint (72.9%), followed by the FT (50%), MT (25%), and MC (23%) joints. Thirty-three (43.4%) horses presented a decline in their OAS, whereas nine (11.8%) presented an improvement from the weanling to yearling age. The radiographic findings suggest that JOCCs are frequent in TB yearlings, but the meaning and relevance of these radiographic findings require further study.

Associations between the radiographic appearance of vascular channels in proximal sesamoid bones, their microstructural characteristics and past racing performance in Thoroughbreds

BACKGROUND

Abnormalities in vascular channel appearance within the proximal sesamoid bone (PSB) are the most common findings in Thoroughbred yearling presale radiographs and are often evaluated on radiographs of adult racehorses. Despite this, their pathogenesis and clinical significance are poorly understood, and associations with racing performance are inconsistent.

OBJECTIVES

To determine microstructural characteristics of the PSBs associated with the radiographic appearance of vascular channels using microcomputed tomography (µCT) and to determine associations with past racing performance in mature horses.

STUDY DESIGN

Cross-sectional.

METHODS

One pair of PSBs were isolated from a forelimb of 59 Thoroughbred racehorses undergoing post-mortem examination. Each PSB (n = 118) was radiographed, assigned a vascular channel grade using previously published and novel grading systems, then imaged using µCT. Associations between radiographic, µCT and performance variables were investigated with uni- and multivariable generalised linear models.

RESULTS

All PSBs had at least one vascular channel (mean 3.6 ± 0.89) observed on µCT originating from the abaxial border, yet in only 63.6% (75/118) were channels observed radiographically. Proximal sesamoid bones with a higher bone volume fraction (odds ratio [OR] 1.08; 95% confidence interval [CI] 1.01-1.15; P = .03) and wider channel diameter (mm) on µCT (OR 20.67; 95% CI 3.29-130.00; P = .001) were more likely to have vascular channels identified on radiographs. Greater radiographic channel number (OR 0.96; 95% CI 0.92-1.00; P = .04) and channel diameter (mm; OR 0.96; 95% CI 0.92-1.00; P = .04) were associated with fewer career placings.

MAIN LIMITATIONS

Radiographs of isolated bones avoided the normal superimposition of tissue encountered in the live horse.

CONCLUSIONS

The ability to identify vascular channels radiographically indicates widening of channels and densification of the PSB. More radiographic channels and greater channel diameter were associated with similar or poorer measures of past performance, suggesting that these changes are not desirable.

Radiological Evaluation of Juvenile osteochondral Conditions in Brazilian Warmblood Horse

The term juvenile osteochondral condition (JOCC) has been used to identify developmental changes in the growth plates. The condition is characterized by a set of changes with similar pathogenesis that affect the immature skeleton and joints of growing foals. The aim of the current study is to investigate the prevalence and degree of severity of osteochondral changes in Brazilian warmblood (BW) foals in two farms in the south of Brazil. Radiological evaluation was applied to the metacarpophalangeal (MCP), carpal (C), metatarsophalangeal (MTP), tarsal (T), and femorotibiopatellar (FTP) joints of 90 foals (47 females and 43 males) in the age group 16-36 months. The evaluation was made before the animals started their athlete performance. Changes were classified as a degree of severity 0 to 4. Changes were diagnosed in 56 foals (58%) that had 105 affected joints. Thirty-three (59%) out of the 56 animals had changes in more than one joint; 57% (19/33) of them had bilateral changes. MTP and MCP were the joints with the most severe changes, respectively (severity 2 and 3), followed by FTP, T, and C. Osteochondral fragments (59%), tarsal arthropathies (48%), irregularities and radiolucency in the FTP joint (7%), and subchondral cystic lesion in the FTP joint (1%), were the most observed changes. BW foals recorded the high prevalence of osteochondral alterations; although MTP and T were the most affected joints, MTP and MCP presented the most severe changes. The present study confirmed significant JOCC prevalence in BW. Further studies should be carried out in different properties.

Osteoarticular radiographic findings of the distal forelimbs in Tbourida Horses

Tbourida is a traditional Moroccan equestrian sport in which 15 horses gallop 200 m in a line while riders fire into the sky with muskets. The stop is the finale and representative demands of this equestrian event. Such particular sudden stop after a fast gallop requires a hyperextension of the metacarpophalangeal joint. Indeed, it is well known that Tbourida show predisposes horses to different injuries of the hard and soft tissues of the distal forelimbs. Yet, there is a paucity of research that examined such lesions. The aim of the present study was to investigate for the first time the type and the prevalence of osteoarticular findings in the distal forelimbs of Tbourida horses using radiographic images. The study was conducted on 127 Tbourida horses aged between 2.5 and 15 years old with 6-year-old horses being the most affected. Data analysis showed that 93,7% of horses exhibit degenerative joint lesions of the fetlock, 86,6% showed ossification of the ungual cartilage, 78,7% had enthesophytes associated with the deep digital flexor tendons, 81,1% had enthesophytes associated with the suspensory ligament branches, and 19,6% showed a particular exostosis on the first phalanx. This large number of lesions reflects how this sport is difficult for horses and also argues that animals are suffering from a lack of welfare and care in their husbandry management.

Ten years of the horse reference genome: insights into equine biology, domestication and population dynamics in the post-genome era

The horse reference genome from the Thoroughbred mare Twilight has been available for a decade and, together with advances in genomics technologies, has led to unparalleled developments in equine genomics. At the core of this progress is the continuing improvement of the quality, contiguity and completeness of the reference genome, and its functional annotation. Recent achievements include the release of the next version of the reference genome (EquCab3.0) and generation of a reference sequence for the Y chromosome. Horse satellite‐free centromeres provide unique models for mammalian centromere research. Despite extremely low genetic diversity of the Y chromosome, it has been possible to trace patrilines of breeds and pedigrees and show that Y variation was lost in the past approximately 2300 years owing to selective breeding. The high‐quality reference genome has led to the development of three different SNP arrays and WGSs of almost 2000 modern individual horses. The collection of WGS of hundreds of ancient horses is unique and not available for any other domestic species. These tools and resources have led to global population studies dissecting the natural history of the species and genetic makeup and ancestry of modern breeds. Most importantly, the available tools and resources, together with the discovery of functional elements, are dissecting molecular causes of a growing number of Mendelian and complex traits. The improved understanding of molecular underpinnings of various traits continues to benefit the health and performance of the horse whereas also serving as a model for complex disease across species.

Influence of Exercise, Age, Body weight, and Growth on the Development of Tarsal Osteoarthritis in Young Mangalarga Marchador Horses

In this study, the effect of early exercise, age, body weight (BW), and growth on the articular cartilage and subchondral bones of the tarsocrural joints was evaluated in 40 young Mangalarga Marchador horses allowed free choice exercise in pasture. Twenty of the horses had additional controlled exercise 3 days per week from a mean age of 30 ± 20 days until 36 months. The training program consisted of an increasing number of 15-minute gallop sprints in an oval paddock with a concrete floor covered by a thick layer of sand. BW, withers height (WH), and neck circumference were measured and body condition scores, cresty neck scores, and obesity index were rated. For each tarsus and foal, 5 standard radiographic projections were evaluated. All evaluations were performed at time point 1 (18 months of age) and time point 2 (36 months of age). Radiographic changes suggestive of tarsal osteoarthritis were observed in two male foals of the trained group at time point 2 (10% of 20). No horses from the untrained group developed OA. Training of the foals did not result in alterations of the morphometric parameters evaluated. However, significant differences were found between time point 1 and 2 in trained and untrained animals. At time point 2, the animals presented greater weights and WHs than at time point 1. We conclude that specific levels of physical activity during initial development do not increase the prevalence of osteoarthritic injury in Mangalarga Marchador foals.

Prevalence, radiographic resolution and outcomes of slab fractures of the third and central tarsal bones in juvenile Thoroughbred horses

BACKGROUND

Veterinarians are required to interpret the significance of radiographic findings for sale, soundness and future racing performance of weanling and yearling Thoroughbreds. We investigated the prevalence and radiographic appearance of slab fractures of the third (T3) and central tarsal (Tc) bones.

METHODS

Weanling and yearling horses with complete or incomplete T3 or Tc fracture were identified by searching a database of radiographs. The prevalence and radiographic appearance at initial diagnosis and after continued pasture turnout, as well as prognosis for racing, of fractures of T3 and Tc were determined.

RESULTS

Fractures were identified in 186 tarsi (184 T3 fracture only, 1 Tc fracture only, 1 Tc and T3 fracture) of 157 horses (126 unilateral T3, 29 bilateral T3, 1 contralateral Tc and T3, 1 unilateral Tc and T3) from 7676 examinations. The prevalence of T3 and Tc fractures was 2.40 (95% CI 2.07, 2.76) and 0.04 (95% CI 0.01, 0.11) per 100 radiographic examinations respectively. Fractures were identified on the D556-65°MPlLO view and occurred by survey examination at 11.1 ± 1.3 months in 85.7% horses. At initial diagnosis, 84.3% of T3 fractures appeared incomplete and involved the distal articular surface. Fracture score improved (P < 0.001), and dorsal modelling (P < 0.001) and osteoarthritis score increased in the distal intertarsal joint (P < 0.001), but not the tarsometatarsal joint, between survey and repository examinations. Fractures healed by repository examination in 71.9% of tarsi if there was > 6 months between examinations. There was no difference in sale price, and horses with T3 fractures had fewer trials when 2 and 3 years old (P = 0.023), yet no difference in other parameters of racing success when 2 or 3 years old compared with controls.

CONCLUSION

Tarsal slab fractures can occur in juvenile Thoroughbreds and most heal with continued pasture turnout of > 6 months. Further investigation is required to determine risk factors and before making firm conclusions regarding the optimal management, prognosis for racing and long-term soundness.

Comparison of the racing performance of Thoroughbreds with versus without osteochondral fragmentation of the accessory carpal bone identified on yearling sales repository radiographs

OBJECTIVE To evaluate 2- and 3-year-old and career race performance of Thoroughbred racehorse prospects with and without osteochondral fragmentation of the accessory carpal bone (ACB) identified on yearling presale radiographs. DESIGN Retrospective, matched cohort study. ANIMALS 47 nonlame Thoroughbreds with (exposed cohort) and 94 nonlame Thoroughbreds without (unexposed cohort) osteochondral fragmentation of ACB facture identified on yearling sales repository radiographs. PROCEDURES Repository radiographic interpretation reports for September yearling sales of a large Kentucky auction house from 2005 through 2012 were reviewed, and race records were collected and analyzed. Race performance was compared between horses with and without ACB fracture chosen from the same sale to identify associations between racing performance and ACB fracture. RESULTS No significant differences were identified between horses with or without ACB fracture in their incidence of starting a race as a 2- or 3-year-old and the number of races started, earnings, or earnings per start for 2- or 3-year-old or career race performance. There was no significant difference in performance between horses with or without concurrent carpal osteoarthritis, nor did performance differ between horses with ACB fracture alone and those with ACB fracture and other radiographic abnormalities found to be associated with poorer performance in previous studies. CONCLUSIONS AND CLINICAL RELEVANCE ACB fracture with or without carpal osteoarthritic changes identified on repository radiographs of Thoroughbred yearlings was not associated with poorer racing performance or lower likelihood of starting a race as a 2- or 3-year-old, compared with outcomes for unaffected horses.

Clinical occurrence and radiographic diagnosis of distal limb lameness in equine

The objectives of this study was to evaluate the hospital occurrence of various radiographic lesions of the distal limb (bones and joints) lameness in equine and to evaluate the role of nerve and joint blocks for the localization of lameness in equine. All the equine lameness cases (117), presented during the one year study period that were subjected to radiographic evaluation, were investigated. Out of these, 20 equine lameness cases were subjected to systematic evaluation including nerve / joint blocks to confirm, whether the clinically or radiographically detectedlesion was the primary cause for the lameness or not. Out of 117, 78 equine (66.67%), were diagnosed with 124 radiographic lesions involving 101 limbs. The majority (62.8%) of the equines had single radiographic lesion, whereas the remaining animals were detected with multiple lesions involving one (15.4%) or more limbs (21.8%). Majority cases of equine lameness were recorded in winter season. Highest per cent lesions were recorded in hoofregion (25.81%) with more common involvement of fore feet (68.75%) and in mares (54.54%). Hock and fetlock regions were second (22.6%) and third (21.8%) most common regions for occurrence of equine lameness. Fetlock joint of hindlimb (63%) was more commonly affected than that of the forelimb. In this study, 16 nerve / joint blocks were applied in 15 horses and these were found helpful in confirming the lameness lesions in 66.7% cases. In conclusion, high prevalence of multiple lesions involving one or more limb poses great diagnostic challenge. Forelimb hoof and the hock were most frequently involved in distal limb lameness in equine. Periostitis and arthritis were most prevalent lameness causing lesions in equine. Physical examinations, nerve/ joint bocks and radiography complement each other in confirming the site of lesion causing lameness.

Radiographic Identification of Osseous Cyst- Like Lesions in the Distal Phalanx in 22 Lame Thoroughbred Horses Managed Conservatively and Their Racing Performance

Reasons for performing study: To investigate the racing performance of Thoroughbred horses with osseous cyst-like lesions (OCLLs) in the distal phalanx causing lameness and treated conservatively. Objectives: To assess horses' ability to race and perform after radiographic identification of OCLL in the distal phalanx of Thoroughbred horses with lameness at the time of detection and undergoing conservative treatment. Study Design: Retrospective case control study. Methods: The clinical database of one equine clinic was reviewed in a 10-year period for Thoroughbreds showing lameness localized to the foot and a radiographic diagnosis of OCLL in the distal phalanx. Sex, age at time of detection of the OCLL, degree of lameness, affected limb, and treatment were recorded. Successful performance of horses was assessed by racing at least once after detection of the OCLL and maximum racing performance rating (RPR). Radiographic features such as size, location, sclerotic rim of the OCLL and irregularity of the articular surface of the distal phalanx were compared to successful performance using univariable statistical analysis. Successful performance of horses with OCLL was compared to a control group of maternal siblings by parametric testing. Results: Twenty-two horses met the inclusion criteria. Thirteen horses raced after the detection of OCLLs. Eight did not race, one case had not yet reached racing age, resulting in 62% (13/21) of racing age racing at least once. The number of successfully performing horses with an OCCL was significantly lower compared to their maternal siblings [p = 0.03, Odds ratio (OR) = 0.30]. If horses with OCLL in the distal phalanx raced, their RPR was similar to their maternal siblings. No significant association was found between radiographic features of OCLLs and successful performance, but OCLLs in the left forelimb carried a more favorable outcome for racing (p = 0.02, OR = 2.33 95%CI 1.27, 4.27) compared to OCLLs in any other limb. Conclusions: Horses with lameness and an OCLL in the distal phalanx managed conservatively are less likely to race when compared to their maternal siblings. If horses with OCLLs in the distal phalanx are able to race, their performance, measured as RPR, was comparable to their maternal siblings. Due to the small numbers in this study the results should be interpreted carefully.

Relationship between repository radiographic findings and subsequent performance of Quarter Horses competing in cutting events

OBJECTIVE To investigate potential associations between repository radiographic findings and subsequent performance of Quarter Horses competing in cutting events. DESIGN Retrospective cohort study. SAMPLE Repository radiographs (ie, radiographs obtained at the time of sale) for 343 client-owned horses. PROCEDURES Repository radiographic findings were compared with objective measures of performance, including the likelihood of competing; the likelihood of earning money as a 3-year-old, as a 4-year-old, and as a 3- and 4-year-old combined; and the amount of money earned as a 3-year-old, as a 4-year-old, and as a 3- and 4-year-old combined. RESULTS The presence of mild osteophytes involving the distal aspect of the tarsal joint was significantly associated with lower mean earnings as a 4-year-old. The presence of osteophytes on the dorsoproximal aspect of the middle phalanx of the hind limbs was significantly associated with an increased odds of earning money as a 4-year-old. Radiographic lesions of the medial femoral condyle of the stifle joint were not significantly associated with subsequent performance. CONCLUSIONS AND CLINICAL RELEVANCE Most abnormalities identified on repository radiographs were not significantly associated with subsequent performance. The significant association between mild tarsal osteophytosis and earnings was unexpected. Results of the present study indicated the need for further investigation of the relationship between radiographic findings and performance outcome in Western performance horses.

Outcome after arthroscopic treatment of lateral femoral trochlear ridge osteochondrosis in sport horses

Objectives: To determine the short- and long-term outcome for sport horses after arthroscopic treatment of osteochondrosis of the lateral trochlear ridge of the femur.

Methods: A retrospective study was performed using the medical records of horses intended for use as English sport horses. Outcome was obtained through telephone questionnaire.

Results: Thirty-seven horses, mainly Warmbloods, underwent arthroscopic surgery for treatment of lateral femoral trochlear ridge osteochondrosis. Short-term outcome revealed that 27 of 37 horses had no complications. Seven horses had postoperative lameness and effusion which eventually resolved in four horses. Long-term outcome was available for 29 horses, of which 19 were performing to full expectations. Five horses were athletic but at a lower level than expected, and five horses were unable to be used. The depth of the lesion was significantly associated with short-term complications of effusion and lameness. The depth and length of the lesion were not associated with the long-term outcome, but involvement of structures other than the lateral trochlear ridge (patella, medial trochlear ridge) was associated with a worse prognosis.

Clinical significance: The prognosis for sport horses following stifle arthroscopy for lateral trochlear ridge is similar to that reported in other studies and lesions at other sites within the stifle joint.

A retrospective study of radiographic abnormalities in the repositories for Thoroughbreds at yearling sales in Japan

This study aimed to evaluate whether radiographic abnormalities at yearling sales were associated with the failure to start racing at 2–3 years of age. Radiographic abnormalities in the carpal (n=852), tarsal (n=976), metacarpophalangeal (n=1,055), and metatarsophalangeal joints (n=1,031) from 1,082 horses, recorded at yearling sale, were reviewed. Eighty-two horses (7.6%) failed to start racing. Radiographic abnormalities such as wedged or collapsed tarsal bones, irregular lucency of a sagittal ridge at the distal aspect of the distal third metatarsal bone, and proximal dorsal fragmentation of the first phalanx in metatarsophalangeal joints were associated with failure to start racing in these horses. In the follow-up survey of 12 horses with one or more these radiographic abnormalities, the horses failed to start racing due to reasons unrelated to these radiographic abnormalities such as pelvic fractures (2 horses), fracture of a distal phalanx (1 horse), cervical stenotic myelopathy and proximal sesamoid fracture (1 horse), superficial digital flexor tendonitis (2 horses), laryngeal hemiplegia (1 horse), economic problems (2 horses) and unknown causes (3 horses). Although radiographic abnormalities at yearling sales can be associated with failure to start racing at 2–3 years of age, these radiographically detected abnormalities might not necessarily cause that failure.

Heritability and prevalence of selected osteochondrosis lesions in yearling Thoroughbred horses

BACKGROUND

Osteochondrosis is considered multifactorial in origin, with factors such as nutrition, conformation, body size, trauma and genetics thought to contribute to its pathogenesis. Few studies have investigated the effects of genetic variability of osteochondrosis in Thoroughbreds.

OBJECTIVES

To describe the prevalence and genetic variability of a subset of osteochondrosis lesions in a group of Thoroughbred yearlings.

STUDY DESIGN

Retrospective cohort study.

METHODS

Radiographs of 1962 Thoroughbred yearlings were retrieved from clinical records obtained between 2005 and 2013. Pedigree information was obtained from the Australian Stud Book. Osteochondrosis lesions were documented in selected joints and estimates of heritability were obtained by fitting linear mixed models in ASREML software.

RESULTS

The overall prevalence of osteochondrosis was 23%. Osteochondrosis was identified in 10% of stifle joints, 6% of hock joints and 8% of fetlock joints. The heritability estimates ranged from 0 to 0.21. The largest estimates were 0.10, 0.14, 0.16 and 0.21 for lesions of the distal intermediate ridge of the tibia, dorso-proximal proximal phalanx (P1), any stifle osteochondrosis, and lesions of the lateral trochlear ridge of the distal femur, respectively. Although calculated heritability estimates had high standard errors, meta-analyses combining the present results with published estimates were significant at 0.10, 0.17, 0.15 and 0.20 for stifle, tarsal, fetlock and these joints combined, respectively. In addition, there was a permanent environment attributable to the dam effect.

MAIN LIMITATIONS

Inclusion criteria were based on radiographic findings in specific joints at a specific age range in Thoroughbreds.

CONCLUSIONS

The present results indicate that only a proportion of osteochondrosis in Thoroughbreds is heritable. The permanent environment effects of the dam were observed to have effects on some categories of osteochondrosis.

A retrospective study of radiographic abnormalities in the repositories of 2-year-old Thoroughbred in-training sales in Japan

This study aimed to evaluate the influence of radiographic abnormalities of 2-year-old Thoroughbred horses that were listed at in-training sales in Japan, on whether they started to race or not at 2–3 years of age. Radiographs of 850 2-year-old Thoroughbreds in the in-training sales repository from 2007 to 2010 were reviewed, and 26 categories of radiographic abnormalities were found. Forty-three horses (5.1%, 43/850) did not start a race at 2–3 years of age. In accordance with the racing results for this age category, as determined by Fisher’s exact test and multiple logistic regression analysis, none of the radiographic abnormalities were significantly related to failure to start a race. At 2 years of age, 198 horses (23.3%, 198/850) did not start a race. Horses with enlargement of the proximal sesamoid bones in the fore (9 of 19 horses) and hind limbs (5 of 9 horses) did not start a race at the age of 2 years, and fewer of these horses (fore, P=0.021; hind, P=0.030) started a race at the age of 2 years compared with the population of horses without these radiographic abnormalities. These results suggest that identification of radiographic enlargement of the proximal sesamoid bones during training sales could derail the racing debut of horses at the age of 2 years. However, this might not necessarily indicate a poor prognosis and resulting in retirement from racing at 2–3 years of age.

Musculoskeletal Pathology

The current understanding of pathology as it relates to common diseases of the equine musculoskeletal system is reviewed. Conditions are organized under the fundamental categories of developmental, exercise-induced, infectious, and miscellaneous pathology. The overview of developmental pathology incorporates the new classification system of juvenile osteochondral conditions. Discussion of exercise-induced pathology emphasizes increased understanding of the contribution of cumulative microdamage caused by repetitive cyclic loading. Miscellaneous musculoskeletal pathology focuses on laminitis, which current knowledge indicates should be regarded as a clinical syndrome with a variety of possible distinct mechanisms of structural failure that are outlined in this overview.

Genome-wide association analysis of osteochondrosis of the tibiotarsal joint in Norwegian Standardbred trotters

Osteochondrosis (OC), a disturbance in the process of endochondral ossification, is by far the most important equine developmental orthopaedic disease and is also common in other domestic animals and humans. The purpose of this study was to identify quantitative trait loci (QTL) associated with osteochondrosis dissecans (OCD) at the intermediate ridge of the distal tibia in Norwegian Standardbred (SB) using the Illumina Equine SNP50 BeadChip whole-genome single-nucleotide polymorphism (SNP) assay. Radiographic data and blood samples were obtained from 464 SB yearlings. Based on the radiographic examination, 162 horses were selected for genotyping; 80 of these were cases with an OCD at the intermediate ridge of the distal tibia, and 82 were controls without any developmental lesions in the joints examined. Genotyped horses descended from 22 sires, and the number of horses in each half-sib group ranged from 3 to 14. The population structure necessitated statistical correction for stratification. When conducting a case-control genome-wide association study (GWAS), mixed-model analyses displayed regions on chromosomes (Equus callabus chromosome - ECA) 5, 10, 27 and 28 that showed moderate evidence of association (P ≤ 5 × 10(-5); this P-value is uncorrected i.e. not adjusted for multiple comparisons) with OCD in the tibiotarsal joint. Two SNPs on ECA10 represent the most significant hits (uncorrected P=1.19 × 10(-5) in the mixed-model). In the basic association (chi-square) test, these SNPs achieved statistical significance with the Bonferroni correction (P=0.038) and were close in the permuted logistic regression test (P=0.054). Putative QTL on ECA 5, 10, 27 and 28 represent interesting areas for future research, validation studies and fine mapping of candidate regions. Results presented here represent the first GWAS of OC in horses using the recently released Illumina Equine SNP50 BeadChip.

Incidence of palmar process fractures of the distal phalanx and association with front hoof conformation in foals

REASONS FOR PERFORMING STUDY

Recent studies indicate a high prevalence of fractures of the palmar processes (PP) of the distal phalanx in foals. However, information on the prevalence of such fractures in different breeds and the effect of predisposing factors, such as hoof conformation, is limited.

OBJECTIVES

To examine the prevalence of distal phalanx PP fractures in foals and report the relationship of distal limb and hoof conformation with the prevalence of fracture.

STUDY DESIGN

Longitudinal study.

METHODS

Front hooves of 19 Thoroughbred, Quarter Horse and Arabian foals were examined. Digital radiographic and photographic images of the distal aspect of the forelimbs were taken at ∼2.5 month intervals. Five radiographic projections of each limb were as follows: lateromedial; horizontal beam dorsopalmar; dorso60°proximal-palmarodistal oblique; dorso60°proximo45°lateral-palmarodistomedial oblique; and dorso60°proximo45°medial-palmarodistolateral oblique. The relationship between measurements and the prevalence of fractures was assessed by 3-way ANOVA.

RESULTS

Fractures were found in 74% (n = 14) of the foals during the study period. The prevalences of lateral PP and medial PP fractures were not significantly different. Several hoof measurements were associated with PP fractures. Longer dorsal length of the distal phalanx was associated with medial PP fractures, while smaller lateral angle and shorter lateral palmar length were associated with a higher prevalence of lateral PP fractures.

CONCLUSIONS

This study revealed a high prevalence of PP fractures in young foals, particularly in Thoroughbred foals. The hoof conformation may be one of the contributory factors to PP fractures in foals.

An assessment of intra- and interobserver agreement of reporting orthopaedic findings on presale radiographs of Thoroughbred yearlings

REASONS FOR PERFORMING STUDY

Radiography is commonly used in clinical practice but agreement of reporting of radiographically detected orthopaedic findings in horses has rarely been studied.

OBJECTIVES

To assess agreement within and between observers for reporting of orthopaedic findings on presale radiographs of Thoroughbred yearlings.

STUDY DESIGN

Retrospective analysis of archived radiographs.

METHODS

Four veterinary radiology specialists each twice examined 167 sets of radiographs for orthopaedic findings in the fore feet, fore and hind fetlocks, carpi, tarsi and stifles. There were 27 findings analysed for agreement. Kappa statistic (κ), percentage of positive agreement (Ppos) and percentage of negative agreement are reported.

RESULTS

An excellent percentage of negative agreement was observed for all findings, with the exception of regular vascular channels of the proximal sesamoid bones. Ppos and κ results were variable. The presence of extra carpal bones, osseous cyst-like lesions of the ulnar carpal bone, sagittal ridge defects of the third metacarpus, fracture of the fore and hind proximal sesamoid bones, regular vascular channels in the hind proximal sesamoids, osteochondrosis lesions of the distal intermediate ridge and/or medial malleoli of the tibia, and osseous cyst-like lesions in the medial femoral condyle was consistently observed with an intra- and interagreement κ≥0.5 and Ppos≥50%. Lucency within the proximal sesamoids consistently had an observed intra- and interagreement κ<0.4 and Ppos<40%.

CONCLUSIONS

Observation of orthopaedic findings on yearling repository radiographs showed generally excellent agreement on the absence of findings, but variable agreement on the presence of findings. Agreement was good for larger and easy to categorise radiographic findings. More accurate definitions and training need to be developed to improve agreement within and between observers for orthopaedic findings with poor or fair to good agreement.

Articular osteochondrosis: a comparison of naturally-occurring human and animal disease

BACKGROUND

Osteochondrosis (OC) is a common developmental orthopedic disease affecting both humans and animals. Despite increasing recognition of this disease among children and adolescents, its pathogenesis is incompletely understood because clinical signs are often not apparent until lesions have progressed to end-stage, and examination of cadaveric early lesions is not feasible. In contrast, both naturally-occurring and surgically-induced animal models of disease have been extensively studied, most notably in horses and swine, species in which OC is recognized to have profound health and economic implications. The potential for a translational model of human OC has not been recognized in the existing human literature.

OBJECTIVE

The purpose of this review is to highlight the similarities in signalment, predilection sites and clinical presentation of naturally-occurring OC in humans and animals and to propose a common pathogenesis for this condition across species.

STUDY DESIGN

Review.

METHODS

The published human and veterinary literature for the various manifestations of OC was reviewed. Peer-reviewed original scientific articles and species-specific review articles accessible in PubMed (US National Library of Medicine) were eligible for inclusion.

RESULTS

A broad range of similarities exists between OC affecting humans and animals, including predilection sites, clinical presentation, radiographic/MRI changes, and histological appearance of the end-stage lesion, suggesting a shared pathogenesis across species.

CONCLUSION

This proposed shared pathogenesis for OC between species implies that naturally-occurring and surgically-induced models of OC in animals may be useful in determining risk factors and for testing new diagnostic and therapeutic interventions that can be used in humans.

Prevalence of abnormal radiographic findings in 2-year-old Thoroughbreds at in-training sales and associations with racing performance

OBJECTIVE

To estimate the prevalence of radiographic abnormalities (lesions) in Thoroughbred racehorses at 2-year-old in-training sales and determine whether these lesions and 1-furlong presale workout times were associated with subsequent racing performance.

DESIGN

Retrospective cohort study.

ANIMALS

953 Thoroughbreds.

PROCEDURES

Repository radiographs of carpal, metacarpophalangeal and metatarsophalangeal (fetlock), stifle, and tarsal (hock) joints were examined. Horses with lesions were classified by lesion type and location. Race performance variables were compared between horses with and without lesions and between horses categorized by 1-furlong presale workout times (< or ≥ 11 seconds).

RESULTS

299 horses had ≥ 1 lesion, and 654 had no lesion detected. Odds of starting a race and of earning money racing were lower for horses with any lesion and lower for horses with proximal phalangeal dorsoproximal articular margin chip fracture, proximal sesamoid bone fracture or sesamoiditis, or wedge-shaped central or third tarsal bones, compared with horses that had no lesion. For horses that raced, proximal phalangeal dorsoproximal articular margin chip fractures were associated with lower lifetime earnings, and flattening of the medial femoral condyle was associated with fewer 3-year-old racing starts, compared with values for horses that had no lesion. Horses with workout times < 11 seconds had greater odds of having lifetime starts, lifetime earnings, and maximum purse above threshold (median) values than did horses with slower workout times.

CONCLUSIONS AND CLINICAL RELEVANCE

No radiographic lesions prevented all affected horses from racing. Among horses that raced, few differences were found in performance for horses with and without lesions.

Association of growth, feeding practices and exercise conditions with the severity of the osteoarticular status of limbs in French foals

The aim of this study was to identify the risk factors for the severity of Juvenile OsteoChondral Conditions (JOCC) in limbs of French foals. Twenty-one farms in Normandy, France, were sampled and enrolled in a cohort study including 378 foals from three breeds, followed from the 8th month of pregnancy of the mares until the foals were approximately 6months old. Data on growth, feeding practices and exercise conditions were regularly collected. The carpus, the front and hind digits, the hock and the stifle of the foals were radiographed at the end of follow-up. JOCC severity in each foal was described using a global appraisal of its osteoarticular status (OAS) depending on the number and the severity of radiographic findings. Of the 378 foals, 53% had a good OAS, 34% had an intermediate OAS and 13% had a poor OAS. The breed (Selle Français and French Trotter Standardbred vs. Thoroughbred), a high girth perimeter at early age and an irregular exercise were significantly associated with a poor OAS. This study contributes to the understanding of the development of JOCC. An increased growth and reduced or irregular physical activity during the first weeks of life would be responsible for more severe lesions. Growth and exercise conditions should be carefully monitored to reduce the prevalence of severe JOCC in foals.

Heritability estimates of tarsocrural osteochondrosis and palmar/plantar first phalanx osteochondral fragments in Standardbred trotters

REASONS FOR PERFORMING STUDY

The pathogenesis of osteochondrosis (OC) and palmar/plantar first phalanx osteochondral fragments (POFs) is multifactorial, but specific knowledge of heritability is limited.

OBJECTIVES

To improve the precision of heritability estimates and to estimate the genetic correlation between tarsocrural OC and POFs in Standardbred trotters. Further aims were to examine whether the prevalence of OC/POFs was different in the American and French lineages that have contributed to the Norwegian population, and if the prevalence was affected by heterozygosity.

STUDY DESIGN

Retrospective cohort study.

METHODS

Categorical data on tarsocrural OC and POFs from 2 radiographic studies performed in 1989 and 2007/2008 (n = 1217) were analysed with sire threshold models that included 230 sires.

RESULTS

Heritability of OC at the distal intermediate ridge of the tibia and/or the lateral trochlear ridge of the talus was estimated at 0.29 ± 0.15. For OC at the distal intermediate ridge of the tibia only, the estimate was 0.40 ± 0.17. Heritability of POFs in all 4 limbs was estimated at 0.23 ± 0.13; for metatarsophalangeal POFs this was 0.26 ± 0.13 and for medial metatarsophalangeal POFs 0.32 ± 0.14. Estimates of genetic correlation between OC and POFs ranged from 0.68 ± 0.27 to 0.73 ± 0.28 but were not significantly different from a zero-genetic correlation. Effects of lineages or heterozygosity were not observed.

CONCLUSIONS AND POTENTIAL RELEVANCE

This study confirmed a moderate to high heritability of tarsocrural OC and POF, providing further evidence of the heritable nature of these diseases. Examination of specific lesions yielded the highest heritability; therefore, breeding programmes and future genome-analysis studies should focus on predilection sites rather than the entire disease complex.

Effects of various presale radiographic findings for yearling Thoroughbreds on 2-year-old racing performance

OBJECTIVE

To determine the effects of various presale radiographic findings for Thoroughbreds sold at a yearling sale on 2-year-old racing performance of those horses.

ANIMALS

397 Thoroughbreds.

DESIGN

Cohort study.

PROCEDURES

Thoroughbreds offered for sale at a Thoroughbred sales facility in Kentucky were selected via a randomization procedure. Effects of various presale radiographic findings on the following measures of 2-year-old racing performance were determined: having started a race and having placed (ie, finished in first, second, or third place) in a race at least once, total amount of money earned, and amount of money earned per start.

RESULTS

Of the 397 horses, 192 (48%) started in at least 1 race during the 2-year-old racing year. The odds of failure to start a race as a 2-year-old were 1.78 times as great for horses with forelimb proximal sesamoid bone osteophytes or enthesophytes as for horses without this finding (95% confidence interval, 1.01 to 3.16). The odds of failure to start a race as a 2-year-old were 2.02 times as great for horses with hind limb proximal phalanx osteochondral fragments as for horses without this finding (95% confidence interval, 0.95 to 4.31), although this result was not significant. Radiographic findings did not have an effect on total amount of money earned, amount of money earned per start, or whether horses placed in a race.

CONCLUSIONS AND CLINICAL RELEVANCE

Presale radiographic detection of forelimb proximal sesamoid bone osteophytes or enthesophytes or hind limb proximal phalanx osteochondral fragments in yearlings were associated with failure to start a race during the 2-year-old racing year in study horses.

The histological appearance of the proximal aspect of the dorsal condylar sagittal ridge of the third metacarpal and metatarsal bone in young warmblood horses: normal appearance and correlation with detected radiographic variations

The objective of this study is to describe the normal histological appearance of the dorsoproximal aspect of the sagittal ridge of the third metacarpal/metatarsal bone in young Warmblood horses, and to compare it to the different radiographic variations (irregular, indentation, lucency, notch) described at this level. A total of 25 metacarpo/metatarsophalangeal joints of 12 Warmblood horses were used. Five samples of each radiographically described group were selected for histological processing. Each category was compared with the normal control group. Each group showed a bone cortex, covered by hyaline cartilage and longitudinally aligned collagen fibres covered by loosely organized connective tissue proximally. The normal and irregular group showed a smooth bone cortex. In the indentation and lucency group, a depression in the cortex was detected. The notch group presented an expansion of the cortex. The collagen fibres and connective tissue were located in the depression in the indentation group whereas the location varied in the lucency and notch group. The radiologic detected differences are translated into detectable histological differences. Further research is warranted to determine whether these variations are developmental or congenital and to evaluate their potential influence on the joint function during hyperextension.