Infanticide, related to a stallion's aggression toward a foal sired by another stallion, and feticide related to a new stallion's aggression and/or pheromonal influence (the Bruce effect) inducing loss of a fetus sired by another stallion, a female's counteraction to infanticide, have been proposed for domestic horses (Equus caballus) in human-managed conditions. The aim of the present study was, in conditions close to natural, to investigate the influence of the natural succession of a harem stallion on the mares' subsequent reproductive performance. In a population of semi-feral Konik polski horses observed for 31 years (reproductive seasons) in 8 bands, harem stallion changed 10 times. These changes involved 26 out of 48 mares and 60 out of 609 observed mare-seasons (MS, a year in which a mare experienced a reproductive event). Binary distribution and log link function were assumed. The marginal model included the classification variable (SCH) and the continuous variables (age of the mare and calendar year of reproductive event (birth of a live foal, abortion, foals lost or barrenness) in a given MS was analyzed with generalized linear mixed model. The reproductive fitness of mares and their reproductive success (foal surviving ≥ 1 year), did not differ between MS with and without SCH. Older females were more likely to stay barren, with chances increasing by 21% with each successive year; and less likely to give birth to a foal (13% decrease of chance), and rear a foal to one year of age (12% decrease of chance). The age did not affect the probability of abortions. Of the 26 MS when mares were pregnant when the stallion had changed, there were 25 healthy foals born. For the entire 31 years of monitoring, no aggression toward any foal was observed and all foals that were born in the harem of a new, succeeding stallion successfully reached adulthood. Due to the lack of incidents of infanticide and the lack of evidence suggesting that the presence of a new harem stallion leads to the termination of pregnancies sired by another stallion, the Bruce effect was not confirmed as a biological strategy to reduce investment in pregnancy and potential infanticide in studied population of semi-feral horses.

中文翻译：

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后宫种马的变化与半野生 Konik polski 马 (Equus caballus) 中雌性的繁殖性能下降无关

杀婴，与一匹种马对另一匹种马所生的小马驹的侵略有关，而杀胎与新种马的侵略和/或信息素影响（布鲁斯效应）有关，导致另一匹种马所生的胎儿丢失，雌性对杀婴的反击，有被提议用于人类管理条件下的家马（Equus caballus）。本研究的目的是在接近自然的条件下，研究后宫种马的自然继承对母马随后的繁殖性能的影响。在 8 个带中观察了 31 年（繁殖季节）的半野生 Konik polski 马种群中，后宫种马变化了 10 次。这些变化涉及 48 匹母马中的 26 匹和 609 个观察到的母马季节中的 60 匹（MS，母马经历繁殖事件的一年）。假设二进制分布和日志链接功能。边际模型包括分类变量（SCH）和连续变量（母马年龄和生殖事件日历年（活马驹出生、流产、马驹丢失或不育）在给定的 MS 中使用广义线性混合模型进行分析. 母马的繁殖适应性及其繁殖成功率（马驹存活 ≥ 1 年），在有和没有 SCH 的 MS 之间没有差异。年长的雌性更有可能保持不育，每年增加 21% 的机会；并且更少可能生小马驹（几率降低 13%），将小马驹饲养到一岁（几率降低 12%）。年龄不影响流产几率。26 匹母马怀孕时的 MS当种马发生变化时，有 25 只健康的小马驹出生了。在整个 31 年的监测中，没有观察到对任何小马驹的攻击，所有出生在新种马后宫的小马驹都成功成年。由于没有杀婴事件，也没有证据表明一匹新的后宫公马的出现会导致另一匹公马终止妊娠，布鲁斯效应未被证实为减少妊娠投资和潜在风险的生物学策略。在研究的半野马种群中杀婴。