Study design for the investigation of likely aetiological factors of juvenile osteochondral conditions (JOCC) in foals and yearlings.

The possible aetiology of osteochondrosis and, to a lesser extent, other developmental orthopaedic diseases or juvenile osteochondral conditions (JOCC), has been intensively investigated. However, most studies have focused on single factors of this multi-factorial disorder, or have been conducted under experimental conditions. This paper aims to present and discuss the scientific background of the BOSAC (Breeding, Osteochondral Status and Athletic Career) research program, a multi-factorial investigation on JOCC risk factors in field conditions. The epidemiology of JOCC in horses born in Normandy between 2002 and 2004 was studied. Horses were subjected to repeated body measurements, blood sampling and locomotion evaluation from birth until yearling sales. A radiographic examination, including 10 views of the limbs, was performed on each subject at approximately 6 and 17months of age. Information on nutrition and management programmes was collected by specialists from visits to the farms and the use of questionnaires. A total of 393 foals of three French breeds were monitored from birth to weaning, and 321 of these remained available for further follow-up, making the study unique as regards both the number of subjects and the variety of information collected. The study was designed to describe the evolution of JOCC, and determine possible early markers, risk factors and prognostic factors with respect to performance. Relevant data, suitable for epidemiological analyses, were collected under various field conditions that reflect current management practices in Normandy, France's main horse breeding region.

Effects of management practices as risk factors for juvenile osteochondral conditions in 259 French yearlings.

Several studies have demonstrated a statistical association between management practices and juvenile osteochondral conditions (JOCC) in foals from birth to 6months of age, but this association has not been investigated in yearlings. The purpose of the current study was to determine the adjusted effects of management practices on the onset and evolution of JOCC in French yearlings. The study sample consisted of 259 yearlings born on 20 stud farms in Normandy. The breeding conditions of these horses were monitored from 6 to 17months. They were radiographed at 6 and 17months to determine their radiographic score (RS) and its evolution. Potential risk factors were investigated using univariate and multivariate analyses. The prevalence of JOCC was 48% at 6months and 42% at 17months. Between 6 and 17months, the RS changed (for better or worse) in 52% of yearlings. The main risk factors leading to deterioration in the RS were traumatic. 'Mixed housing' during winter, pastures with rough ground and a bad RS at 6months were significantly associated with deterioration in RS between 6 and 17months. In the multivariate analysis, the breed was not significantly associated with any evolution in the yearlings' RS. This study provides some indications on protective measures to prevent the worsening of JOCC lesions between 6 and 17months, a crucial period since it precedes the sale of yearlings and the beginning of training.

A reliable severity scoring system for radiographic findings in the limbs of young horses.

The validity of methods used to score the severity of radiographic findings (RFs) in horses is uncertain since only one or two joints are usually studied, classification criteria are heterogeneous and the internal validity is not assessed. The aim of this study was to assess the internal validity of a severity scoring system (SSS) of RFs by repeated scoring of a sample of radiographs. This SSS of RFs is based on four criteria that can be applied to every type of RF observed in limb joints. It consists of five weighted severity indexes (0, 1, 2, 4, 8) and was used to assess RFs found on the limbs of 392 young horses. The internal validity of the SSS was assessed using Kappa coefficients calculated on a subsample of 137 horses whose radiographs were interpreted twice. The final RF severity indices from these radiographs were obtained after three experienced veterinarians had reached a consensus, similar to the procedure used at foal and yearling sales. The majority of RFs from the 392 horses were scored either 1 or 2, while scores of 8 were only observed in the stifle and tarsus. Among the subsample, the overall agreement on the presence or absence of RFs was good (κ=0.63; 95% Confidence Interval [CI], 0.56-0.69), and was excellent for the severity of RFs (weighted κ=0.82; 95% CI, 0.75-0.87). Most disagreements involved RFs that scored 1. The fore fetlock and the carpus experienced the lowest agreement. The SSS was a stable and reliable procedure applicable to any RF on any limb joint of the horse. It will be of potential interest in clinical practice and in the pre-purchase evaluation of young horses and could also be used in additional studies on the evolution or risk factors of RFs.

Influence of juvenile osteochondral conditions on racing performance in Thoroughbreds born in Normandy.

The relationship between osteoarticular status and future athletic capacity is commonly accepted in equine practice, but there is little to support this belief in Thoroughbreds. The objective of this study was to assess the prevalence of juvenile osteochondral conditions (JOCC) in Thoroughbred yearlings and to investigate the significance of these with regard to subsequent racing performance. The radiographic files from 328 Thoroughbred yearlings born in Normandy were assessed in a consistent manner and entered into a database together with racing records. Logistic regression models were used to quantify the association between each radiographic parameter and racing performance (raced/not raced, placed/not placed, performer/not performer) at 2, 3, 4 and 5years of age. The front fetlock (30.2% of horses), the dorsal aspect of the hind fetlock (18%), the carpus (15.9%) and the distal part of the hock (15.5%) were the most commonly affected joints. Most horses (87.5%) raced either in turf flat races or in hurdle races. Starting a race at 2years old was more frequent for yearlings without radiographic findings (RF) on the carpus or with less than one RF of moderate severity. The proportions of horses placed at 3years old decreased with increasing number or severity of RF. In racing horses, there was no association between the presence of RF and earnings. The radiographic score, calculated as the sum of all the severity indices found on the radiographic file of the horse appeared well correlated with performance. Using this synthetic index might help veterinarians to evaluate radiographs of Thoroughbred yearlings for potential buyers.

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.

Sub-clinical diseases affecting performance in Standardbred trotters: diagnostic methods and predictive parameters.

The objectives of this study were to determine the prevalence of sub-clinical diseases in poorly-performing Standardbred horses, compare their physiological response to exercise with control horses, and identify predictive parameters of poor-performance. Fifty horses underwent thorough clinical and ancillary examinations, including haematological and biochemical evaluation, Doppler echocardiography, standardised exercise tests (SETs) on both treadmill and racetrack, treadmill video-endoscopy and collection of respiratory fluids. Most of the poorly-performing horses exhibited many concomitant diseases. The most frequently diagnosed problems involved the lower and upper respiratory tract and the musculoskeletal system. Poor-performers had lower speeds at a blood lactate (LA) concentration of 4mmol/L (V(LA4)) and a heart rate (HR) of 200bpm (V(200)) on treadmill and racetrack, as well as lower values for haematological parameters, plasma angiotensin-converting enzyme and antioxidants, compared to control horses. Problems of the respiratory system were the most frequently diagnosed sub-clinical diseases affecting performance. SETs, together with some blood markers, may be useful as a non-specific diagnostic tool for early detection of diseases that may affect performance.