Testing optimal methods to compare horse postures using geometric morphometrics

The study of animal behavior, especially regarding welfare, needs the development of tools to identify, quantify and compare animal postures with interobserver reliability. While most studies subjectively describe animal postures, or quantify only limited parts of the body, the usage of geometric morphometrics has allowed for the description of horses’ and pigs’ upper body outline and the comparison of postures from different populations thanks to robust statistical analysis. We have attempted here to optimize the geometric morphometrics (GM) method already used in horses by introducing the outline analysis with sliding semilandmarks (SSL), by eliminating the balance movement of the neck and by focusing only on parts of the upper line. For this purpose, photographs of 85 horses from 11 riding schools, known for differing in terms of housing and working conditions, were analyzed with previous and new GM methods and these results were compared with each other. Using SSL and eliminating the neck movement appeared to better discriminate the horse populations than the previous GM method. Study of parts of the dorsum proved efficient too. This new methodology should now be used to examine if posture could be an indicator of horse welfare state, and similar studies should be performed in other species in order to validate the same methodology.

动物行为研究，尤其是涉及福利的相关研究，亟需开发可用于识别、量化并比较动物姿态且具备观察者间信度的工具。当前多数研究要么仅对动物姿态进行主观描述，要么仅量化身体的有限部位，而几何形态测量学（geometric morphometrics, GM）的应用则已实现对马与猪的上半身轮廓的描述，并借助稳健的统计分析完成不同种群间的姿态对比。本研究尝试对已应用于马匹的几何形态测量学方法进行优化：引入滑动半标记（sliding semilandmarks, SSL）的轮廓分析方法，消除颈部的平衡运动干扰，且仅聚焦于背侧上线的部分区域。为此，我们分析了来自11家马术学校的85匹马的影像数据——这些学校的饲养与工作条件存在显著差异——并分别采用原有与改进后的几何形态测量学方法进行处理，随后对两种方法的结果展开对比。结果显示，相较于原有方法，引入滑动半标记并消除颈部运动干扰的方式能够更有效地区分不同马群。对背侧上线部分区域的分析同样展现出良好效果。该新型方法后续可用于探究姿态是否可作为马匹福利状态的评估指标，同时也应在其他物种中开展同类研究以验证该方法的普适性。