Bussiman Fernando, Richter Jennifer, Hidalgo Jorge, Silva Fabyano Fonseca E, Ventura Ricardo Vieira, Carvalho Rachel Santos Bueno, Mattos Elisângela Chicaroni, Ferraz José Bento Sterman, Eler Joanir Pereira, de Carvalho Balieiro Júlio Cesar
Animal Nutrition and Production Department, University of São Paulo, Pirassununga, São Paulo, Brazil.
Animal and Dairy Science Department, University of Georgia, Athens, Georgia, USA.
J Anim Breed Genet. 2025 Sep;142(5):463-477. doi: 10.1111/jbg.12919. Epub 2024 Dec 19.
Gait visual scores are widely applied to horse breeding because they are a fast and easy phenotyping strategy, allowing the numeric interpretation of a complex biological process such as gait quality. However, they may suffer from subjectivity or high environmental influence. We aimed to investigate potential causal relationships among six visual gait scores in Campolina horses. The data included 5475 horses with records for at least one of the following traits: Dissociation (Di), Comfort (C), Style (S), Regularity (R), Development (De), and Gait total Scores (GtS). The pedigree comprised three generations with 14,079 horses in the additive relationship matrix. Under a Bayesian framework, (co)variance components were estimated through a multitrait animal model (MTM). Then, the inductive causation algorithm (IC) was applied to the residual (co)variance matrix samples. The resulting undirected graph from IC was directed in 6 possible causal structures, each fitted by a structural equation model. The final causal structure was chosen based on deviance information criteria (DIC). It was found that S significantly impacts the causal network of gait, directly and indirectly affecting C. The indirect causal effect of S on C was through the direct effect of S on De, then the direct effect of De on R, and finally, the direct effect of R on C. Di was caused by S, which is the reason for the genetic correlation between Di and GtS, due to causal effects being added to the model, they absorb the genetic correlation between Di and GtS. Those paths have biological meaning to horse movements and can help breeders and researchers better understand horses' complex causal network of gait.
步态视觉评分在马匹育种中广泛应用，因为它们是一种快速且简便的表型分析策略，能够对诸如步态质量这样复杂的生物学过程进行数值解读。然而，它们可能存在主观性或受环境影响较大的问题。我们旨在研究坎波拉马六种视觉步态评分之间潜在的因果关系。数据包括5475匹马，这些马至少有以下一种性状的记录：分离度（Di）、舒适度（C）、风格（S）、规律性（R）、发育情况（De）和步态总分（GtS）。系谱包含三代，共14,079匹马，用于构建加性关系矩阵。在贝叶斯框架下，通过多性状动物模型（MTM）估计（协）方差分量。然后，将归纳因果算法（IC）应用于残差（协）方差矩阵样本。IC算法得到的无向图被定向为6种可能的因果结构，每种结构都用结构方程模型进行拟合。基于偏差信息准则（DIC）选择最终的因果结构。结果发现，S对步态因果网络有显著影响，直接和间接地影响C。S对C的间接因果效应是通过S对De的直接效应，然后De对R的直接效应，最后R对C的直接效应实现的。Di由S引起，这就是Di与GtS之间遗传相关性的原因，由于因果效应被纳入模型，它们吸收了Di与GtS之间的遗传相关性。这些路径对马匹运动具有生物学意义，有助于育种者和研究人员更好地理解马匹复杂的步态因果网络。
