Quantifying the effect of Warmblood Fragile Foal Syndrome on foaling rates in the German riding horse population.
Authors: Wobbe Mirell, Reinhardt Friedrich, Reents Reinhard, Tetens Jens, Stock Kathrin F
Journal: PloS one
Summary
# Editorial Summary: Warmblood Fragile Foal Syndrome and Reproductive Performance Warmblood Fragile Foal Syndrome (WFFS), a recessive connective tissue disorder caused by a PLOD1 gene mutation, has become a significant concern for breeding programmes since a high-profile case in 2018 and the availability of genetic testing since 2013. Researchers analysed nearly 400,000 coverings and foaling records from ten German studbooks between 2008 and 2020 to quantify the reproductive impact of carrier status, using variance analysis and mixed linear models to account for multiple variables. WFFS carrier stallions produced approximately 2.7% fewer foals than non-carrier sires when mated to an average mare population—a reduction closely matching the theoretical 2.4–3.7% predicted by Hardy–Weinberg equilibrium based on observed carrier frequencies of 9.5–15.0%. Interestingly, carrier stallions showed indications of favourable dressage performance, suggesting potential selection pressure toward carriers despite their reproductive cost. For practitioners involved in breeding decisions, these findings underscore the importance of genetic testing and studbook reporting; the actual impact likely exceeds these figures because recorded WFFS cases represent only confirmed diagnoses, whilst silent losses from carrier-to-carrier matings remain undetected and unaccounted in foaling statistics.
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Practical Takeaways
- •Use available PLOD1 genetic testing to identify carrier stallions; accepting a ~2.7% reduction in foaling rates may be offset by performance benefits in some breeding programmes
- •Breeders should track premature foal losses and early foal deaths as these represent undiagnosed WFFS cases beyond registered cases
- •Studbook data and genetic testing integration enables population-level monitoring of hereditary disorders; maintain and expand these reporting systems
Key Findings
- •WFFS carrier stallions showed 2.7% lower average foaling rates compared to WFFS-free sires when mated to average mare populations
- •Carrier frequency of WFFS in Warmblood horses ranges from 9.5-15.0% based on Hardy-Weinberg principle predictions
- •WFFS carriers demonstrated indications of favorable dressage performance traits despite reproductive disadvantages
- •Reported WFFS cases represent only a fraction of actual premature foal losses attributable to the mutation