在过去,小的种群规模和不平等的祖先贡献导致弗利西亚马的近亲繁殖率很高(ΔF)。二十年前,该研究手册实施了交配配额,并开始发布个人亲属关系,并将ΔF降低到每代1%以下。然而,从那以后,育种种群规模已经减少,这提出了一个问题,即当前的育种策略是否足以使ΔF保持在所需速率以下。本研究的目的是(1)反思过去的近亲繁殖趋势及其主要决定因素,使用谱系分析和(2)使用随机模拟评估当前和其他育种策略的有效性。我们估计当前的ΔF(2013-2022)为每代0.72%。虽然前10名父亲对每年后代数量的总贡献从1980年的75%下降到2022年的35%,但这主要是由于批准的学生人数增加,而不是因为父亲之间的贡献更加平等。在模拟育种策略中,只选择平均亲属关系低于平均水平的种马(即,“平均亲属关系选择”)最有效地降低了ΔF(从0.66%降至0.33%)。仅在应用交配配额时,增加繁殖父亲的数量才会产生影响。然而,其效果仍然有限。例如,a~1.5倍增加,再加上每个父亲每年80个后代的交配配额,将ΔF从0.55%降低到0.51%。当增加繁殖母马的数量时,对于ΔF的有意义的降低,需要实际上不可行的大幅增加(例如,需要两倍的母马来将ΔF从0.66%降低到0.56%)。分层交配配额,一种新颖的方法,在这种方法中,我们根据其与最近出生的小马驹的平均亲属关系为每个父亲分配了一个交配配额(每年60、80、100或120个后代)。导致ΔF(0.43%)低于每个父亲每年90个后代的一般交配配额(0.55%)。总的来说,当当前ΔF低于1%时,我们建议实施其他策略,以进一步将弗利西亚马种群的ΔF降低至0.5%以下。对于这个品种和类似的种群,我们建议关注基于亲属关系水平的育种策略,以有效降低ΔF。
In the past, small population sizes and unequal ancestor contributions have resulted in high inbreeding rates (ΔF) in the Friesian horse. Two decades ago, the studbook implemented a mating quota and started publishing individual kinships and reduced ΔF below 1% per generation. However, since then, the breeding population size has decreased and this raises the question whether current breeding strategies are sufficient to keep ΔF below desired rates. The aim of this study was to (1) reflect on past inbreeding trends and their main determinants, using pedigree analysis and (2) evaluate the effectiveness of the current and additional breeding strategies using stochastic simulations. We estimated the current ΔF (2013-2022) at 0.72% per generation. While the total contribution of the top 10 sires to the number of offspring per year has decreased from 75% in 1980 to 35% in 2022, this was mainly due to an increased number of approved studbook sires, and not due to more equalized contributions among sires. Of the simulated breeding strategies, selecting only breeding stallions with a below average mean kinship (i.e., \"mean kinship selection\") was most effective to decrease ΔF (from 0.66% to 0.33%). Increasing the number of breeding sires only had an effect when also a mating quota was applied. However, its effect remained limited. For example, a ~1.5 fold increase, combined with a mating quota of 80 offspring per sire per year, reduced ΔF from 0.55% to 0.51%. When increasing the number of breeding mares, a practically unfeasible large increase was needed for a meaningful reduction in ΔF (e.g. twice as many mares were needed to reduce ΔF from 0.66% to 0.56%). Stratified mating quotas, a novel approach in which we assigned each sire a mating quota (of 60, 80, 100 or 120 offspring per year) based on its mean kinship to recently born foals, resulted in a lower ΔF (0.43%) than a general mating quota of 90 offspring per sire per year (0.55%). Overall, while the current ΔF is below 1%, we recommend to implement additional strategies to further reduce ΔF below 0.5% in the Friesian horse population. For this breed and similar populations, we recommend to focus on breeding strategies based on kinship levels to effectively reduce ΔF.