Department of Gamete and Embryo Biology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, Poland.
University of Warmia and Mazury, Department of Horse Breeding, Faculty of Animal Bioengineering, Olsztyn, Poland.
Theriogenology. 2020 Jul 15;151:1-6. doi: 10.1016/j.theriogenology.2020.03.033. Epub 2020 Mar 26.
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.
杀婴，与种马对另一匹种马所生幼驹的攻击性有关，以及胎杀，与新种马的攻击性和/或信息素影响（布鲁斯效应）导致另一匹种马所生胎儿流产有关，已被提出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，研究发情群种马的自然更替对母马随后繁殖性能的影响。在一个经过 31 年（繁殖季节）观察的半野生波兰马科尼克马种群中，发情群种马发生了 10 次变化。这些变化涉及 48 匹母马中的 26 匹，以及 609 个观察到的母马季节（MS，一匹母马经历繁殖事件的一年）中的 60 匹。采用二元分布和对数链接函数。边际模型包括分类变量（SCH）和连续变量（母马年龄和繁殖事件的日历年份（活驹出生、流产、驹丢失或不育））。在给定的 MS 中，使用广义线性混合模型分析了生育力的边际模型。母马的生殖适应性及其生殖成功率（存活≥1 年的幼驹）在有和没有 SCH 的 MS 之间没有差异。年龄较大的母马更有可能不育，每增加一年生育的机会增加 21%；而分娩幼驹的机会减少（减少 13%），并将幼驹抚养至 1 岁的机会减少（减少 12%）。年龄不影响流产的概率。在 26 个母马在种马更换时怀孕的 MS 中，有 25 个健康的幼驹出生。在监测的 31 年中，没有观察到对任何幼驹的攻击行为，所有在新的、接替的种马的发情群中出生的幼驹都成功地成年。由于没有杀婴事件发生，也没有证据表明新的发情群种马的存在会导致另一匹种马所生的妊娠终止，因此布鲁斯效应没有被证实为减少妊娠投资和潜在杀婴的生物学策略在研究的半野生马种群中。
