Heritability and prevalence of selected osteochondrosis lesions in yearling Thoroughbred horses.
Authors: Russell J, Matika O, Russell T, Reardon R J M
Journal: Equine veterinary journal
Summary
# Editorial Summary Osteochondrosis affects roughly one in four Thoroughbred yearlings, with prevalence varying by joint—10% in the stifle, 8% in the fetlock, and 6% in the hock—yet Russell and colleagues' analysis of radiographs from 1,962 yearlings (2005–2013) reveals that genetic factors account for only a modest proportion of this disease burden. Using pedigree data and linear mixed models, heritability estimates ranged from 0 to 0.21 across different lesion sites, with the most heritable lesions being those of the lateral trochlear ridge of the distal femur (h² = 0.21) and the dorso-proximal proximal phalanx (h² = 0.16). Whilst individual heritability estimates carried substantial standard errors, meta-analyses incorporating published data strengthened confidence in estimates around 0.10–0.20 across joint regions, and notably, maternal permanent environmental effects were demonstrated for certain osteochondrosis presentations. For practitioners seeking to reduce osteochondrosis through selective breeding, these findings suggest genetic selection alone will have limited impact; instead, attention to modifiable risk factors—nutrition, rearing practices, conformation assessment, and exercise management—likely offers greater opportunity to influence disease prevalence in the next generation.
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Practical Takeaways
- •Osteochondrosis in Thoroughbreds is only partially heritable; breeding decisions should account for the substantial non-genetic environmental and nutritional factors contributing to disease
- •Management of pregnant mares and young yearlings should focus on nutrition, conformation assessment, and trauma prevention since maternal and environmental effects significantly influence lesion development
- •Radiographic screening of yearlings in high-risk joints (stifle, hock, fetlock) can identify affected animals early, allowing for targeted management before athletic training begins
Key Findings
- •Overall prevalence of osteochondrosis in Thoroughbred yearlings was 23%, with stifle affected in 10%, hock in 6%, and fetlock in 8%
- •Heritability estimates ranged from 0 to 0.21, with lateral trochlear ridge of distal femur showing the highest estimate at 0.21
- •Meta-analyses combining present results with published estimates showed significant heritability for stifle (0.10), tarsal (0.17), fetlock (0.15), and combined joints (0.20)
- •Permanent environmental effects attributable to the dam were observed to influence some categories of osteochondrosis