Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan.
Wildlife Research Center, Kyoto University, Kyoto, Japan.
PLoS One. 2022 Jul 21;17(7):e0271535. doi: 10.1371/journal.pone.0271535. eCollection 2022.
Maternal aging has negative influences on the development and racing performance of their offspring in racehorses. However, the mechanism by which pregnancy at old age reduces the race performance of the offspring is unknown. Here, two hypotheses were posited: 1) Foals born to older mares are more likely to have muscular, skeletal, and cognitive disadvantages (direct effects). 2) Foals born to older mares are more likely to be affected by non-physiological factors correlating with the mare's age, such as the quality of sires (e.g. low-quality sires are likely to be chosen as partners of older broodmares). To test these hypotheses, the effect of the broodmare's age on the offspring's racing performance was examined, while controlling for the effects of the stallion's quality, age, and ID, offspring's sex, trainer, and the location of the training center. Information of racehorses registered to the Japan Racing Association were collected from the Japan Bloodhorse Breeders' Association website. Overall, results showed that the racing performance of horses born from older mares was lower than that of horses born from younger mares. However, generalized linear mixed models (GLMM) indicated that the quality of sires was significantly associated with the offspring's racing performance, rather than the broodmare's age itself. Furthermore, the age of broodmares was negatively correlated with the quality of sires, although the variance inflation factor was low. Therefore, the effect of maternal aging was negligible or only limited, and rather, the sire's quality had an important influence on the offspring's racing performance. Low quality sires, or cheap stallions in other words, are likely to be chosen as partners of older blood-mares, which may have reproductive risks such as lower fertility and higher rate of miscarriages. The present study suggests that the conventional belief that racehorses born from older mares show lower performance may not always be accurate.
母马老化对赛马的后代发育和比赛表现有负面影响。然而，高龄妊娠降低后代比赛表现的机制尚不清楚。在这里，提出了两个假设：1）老年母马所生的小马更有可能在肌肉、骨骼和认知方面存在劣势（直接影响）。2）老年母马所生的小马更有可能受到与母马年龄相关的非生理因素的影响，例如种马的质量（例如，低质量的种马可能被选为老年母马的伴侣）。为了检验这些假设，本研究考察了母马年龄对后代比赛表现的影响，同时控制了种马的质量、年龄和 ID、后代的性别、教练和训练中心的位置的影响。从日本赛马协会网站上的日本赛马育种者协会收集了注册赛马的信息。总体而言，结果表明，老年母马所生的马的比赛表现低于年轻母马所生的马。然而，广义线性混合模型（GLMM）表明，种马的质量与后代的比赛表现显著相关，而不是母马的年龄本身。此外，尽管方差膨胀因子较低，但母马的年龄与种马的质量呈负相关。因此，母马老化的影响可以忽略不计或仅限于有限，而种马的质量对后代的比赛表现有重要影响。质量较低的种马，或者换句话说，廉价的种马，更有可能被选为老年母马的伴侣，这可能会带来繁殖风险，例如生育力降低和流产率升高。本研究表明，传统上认为老年母马所生的赛马表现较低的观点并不总是准确的。
