Inbreeding is caused by mating between related individuals and is associated with reduced fitness and performance (inbreeding depression). Several studies have detected heterogeneity in inbreeding depression among founder individuals. Recently, a procedure was developed to predict hidden inbreeding depression load that is associated with founders using the Mendelian sampling of non-founders. The objectives of this study were to: (1) analyse the population structure and general inbreeding, and (2) test this recent approach for predicting hidden inbreeding depression load for four morphological traits and two morphology defects in the Pura Raza Española (PRE) horse breed. The regression coefficients that were calculated between trait performances and inbreeding coefficients demonstrated the existence of inbreeding depression. In total, 58,772,533 partial inbreeding coefficients (Fij) were estimated for the whole PRE population (328,706 horses). We selected the descendants of horses with a Fij ≥ 6.25% that contributed to at least four offspring and for which morphological traits were measured for the subsequent analysis of inbreeding depression load (639 horses). A pedigree was generated with the last five generations (5026 animals) used as the reference population (average inbreeding coefficient of 8.39% and average relatedness coefficient of 10.76%). Heritability estimates ranged from 0.08 (cresty neck) to 0.80 (height at withers), whereas inbreeding depression load ratios ranged from 0.01 (knock knee) to 0.40 (length of shoulder), for an inbreeding coefficient of 10%. Most of the correlations between additive and inbreeding depression load genetic values and correlations between inbreeding depression load genetic values for the different traits were positive or near 0. Although the average inbreeding depression loads presented negative values, a certain percentage of the animals showed neutral or even positive values. Thus, high levels of inbreeding do not always lead to a decrease in mean phenotypic value or an increase in morphological defects. Hence, individual inbreeding depression loads could be used as a tool to select the most appropriate breeding animals. The possibility of selecting horses that have a high genetic value and are more resistant to the deleterious effects of inbreeding should help improve selection outcomes.

中文翻译：

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Pura Raza Española 马形态特征和缺陷的遗传近交抑制负荷


近交是由相关个体之间的交配引起的，并且与适应性和表现下降（近交衰退）有关。几项研究已经发现创始人个体之间近亲繁殖抑郁症的异质性。最近，开发了一种程序来使用非创始人的孟德尔抽样来预测与创始人相关的隐性近交衰退负荷。本研究的目的是：(1) 分析种群结构和一般近交，以及 (2) 测试这种最新方法，用于预测 Pura Raza Española (PRE) 马的四个形态特征和两个形态缺陷的隐性近交衰退负荷品种。计算性状表现与近交系数之间的回归系数，证明了近交衰退的存在。总体而言，整个 PRE 种群（328,706 匹马）的部分近交系数 (Fij) 被估计为 58,772,533 个。我们选择了 Fij ≥ 6.25% 的马的后代，这些马的后代至少有 4 个后代，并测量了其形态特征，用于随后的近交抑郁负荷分析（639 匹马）。以最后五代（5026只动物）作为参考种群（平均近交系数为8.39％，平均相关系数为10.76％）生成谱系。遗传力估计范围为 0.08（颈嵴）至 0.80（肩高），而近交抑郁负荷比范围为 0.01（内翻膝）至 0.40（肩长），近交系数为 10%。大多数加性和近交抑郁负荷遗传值之间的相关性以及不同性状的近交抑郁负荷遗传值之间的相关性均为正或接近0。 尽管平均近交抑郁负荷呈现负值，但一定比例的动物呈现中性甚至正值。因此，高水平的近交并不总是导致平均表型值的降低或形态缺陷的增加。因此，个体近交抑制负荷可以用作选择最合适的繁殖动物的工具。选择具有高遗传价值并且对近亲繁殖的有害影响更具抵抗力的马的可能性应该有助于改善选择结果。