现代赛马选择性育种在推动速度提升的同时，也导致了种群基因多样性的严重衰退。[1]1973年传奇赛马Secretariat在Belmont Stakes中以2分24秒的成绩获胜，领先第二名31个马身，这一纪录半个世纪以来无人打破。[1]尽管自此以后投入了数十亿美元进行育种和训练，但该纪录至今未被超越，反映出现代赛马已接近生物学意义上的速度极限。[1]
遗传多样性的丧失是这一瓶颈形成的根本原因。[1]现代95%的纯血马都下传自18世纪进口的三匹阿拉伯马中的一匹——Darley Arabian。[1]在澳大利亚的13.5万匹纯血马中，80%的近交来自仅有的十个18世纪祖先。[1]这种极度限制的遗传基础严重阻碍了进一步的性能提升。从19世纪中期到1910年左右，赛马速度曾有过显著改进，1.5英里赛程在这段时期快了2至4秒，相当于1-2%的提升，但此后改进幅度已大幅放缓。[1]
为了突破这一生物学限制，新的技术手段开始被引入。[1]2024年阿根廷公司Kheiron宣布首次通过CRISPR基因编辑技术对马匹进行遗传改造，目标是修改MSTN基因以增加爆发性速度。[1]这一基因存在两种变异形式：携带"C"版本的马匹倾向于短距离冲刺能力，而"T"版本则倾向于长距离耐力。[1]值得注意的是，Secretariat死后解剖发现其心脏约重10公斤，是正常体重的两倍，但这一显著的生理优势未能可靠地遗传给后代。[1]
Modern thoroughbred horse racing faces a fundamental biological constraint rooted in decades of selective breeding for speed. In 1973, the legendary racehorse Secretariat won the Belmont Stakes in 2 minutes and 24 seconds, finishing 31 lengths ahead of the competition—a record that has remained unbroken for half a century despite billions of dollars invested in breeding and training [1]. The closest challenge came in 1989 when Easy Goer achieved a time of 2 minutes and 26 seconds, two seconds slower than Secretariat's mark [1].
The pursuit of racing performance has dramatically narrowed the genetic foundation of modern thoroughbreds. Approximately 95 percent of today's purebred racing horses descend from just one of three Arabian stallions imported in the 18th century—the Darley Arabian [1]. This extreme genetic concentration is evident in breeding records: among Australia's 135,000 purebred horses, 80 percent of their close relatives trace back to only ten ancestors from the 18th century [1]. Between the mid-19th century and around 1910, racing times improved by only 1 to 2 percent over 1.5-mile courses—a gain of roughly 2 to 4 seconds [1]. This plateauing improvement suggests that decades of artificial selection have brought racehorses close to their biological speed limits.
Contemporary efforts to overcome these constraints have turned to genetic engineering. In 2024, an Argentine company called Kheiron announced the first successful use of CRISPR gene editing on horses, modifying the MSTN gene to increase explosive speed [1]. The MSTN gene exists in two variants: the "C" version typically supports short-distance sprinting, while the "T" version favors long-distance endurance [1]. Interestingly, Secretariat's exceptional performance may have been linked to an unusually enlarged heart—autopsy measurements revealed it weighed approximately 10 kilograms, roughly double the normal size [1]. However, this distinctive trait has not reliably passed to his offspring, highlighting the complexity of translating individual genetic advantages into heritable breeding traits [1].