Abstract
SummaryBackgroundOsteochondrosis 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.ObjectivesTo describe the prevalence and genetic variability of a subset of osteochondrosis lesions in a group of Thoroughbred yearlings.Study designRetrospective cohort study.MethodsRadiographs 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.ResultsThe 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 limitationsInclusion criteria were based on radiographic findings in specific joints at a specific age range in Thoroughbreds.ConclusionsThe 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.
Highlights
Osteochondrosis is a common cause of lameness and joint effusion in the horse [1,2] and may lead to reduced athletic performance [3,4]
Prevalence and heritability estimates for osteochondrosis vary among breeds [10,11,12,13], which suggests the existence of genetic variability in disease susceptibility among breeds [14]
Osteochondrosis lesions in stifle joints were identified in 10% of horses, with the most common site being the lateral trochlear ridge of the distal femur (6% of horses)
Summary
Osteochondrosis is a common cause of lameness and joint effusion in the horse [1,2] and may lead to reduced athletic performance [3,4]. Previous studies have reported a genetic control of osteochondrosis or other factors that lead to this condition [6,8,9]. Studies have shown osteochondrosis to be heritable in some predilection sites in Hanoverian Warmblood horses [10] and Standardbred trotters [11]. A study in Thoroughbreds examining quantitative trait loci for osteochondrosis, in conjunction with clinically diagnosed (radiographs and arthroscopy) cases, was unable to identify significant heritability, which may have been related to a lack of power [14]. Another study of Thoroughbreds, conducted using data derived from radiographic reports, described a significant genetic component to osteochondrosis [15]
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