Geometric morphometrics of face profile across horse breeds and within Arabian horses: Horse face geometric morphometrics.
Abstract: Horse traits under selection are largely quantitative and affected by multiple genes. Horse face shape is an example of a continuous trait, which due to the reliance on observational assessments, is classified into; "dished", "straight", and "roman-nosed". This categorization is often inadequate to convey the full spectrum of the face shape variation especially for genetic studies. The first objective of the current study was to use geometric morphometric methods to quantitatively phenotype face shapes and examine its variation across horse breeds. The second objective was to analyze the face shape variation within Arabian horses since face shape is (1) favored, valued, and genetically selected in certain lineages (e.g. Egyptian), (2) is evaluated by registries and scored in shows, and (3) in its extreme forms pose health concerns. We digitized landmarks on lateral profile photos, particularly on the dorsal curvature of the rostrum, and subjected these landmarks to Generalized Procrustes Analysis to generate independent shape and size variables which were statistically compared across breeds and within Arabians. Horse breeds varied in nasal curvature, ranging from extremely concave to extremely convex, with over 70% of horse breeds exhibiting intermediate concavity (i.e., straight profile). Interestingly, Arabian horses possessed the highest diversity in face profile and individuals clustered into three distinct shape sub-groups (one dished and two straight profile clusters). Our quantitative phenotyping method can be the basis of future genetic studies of facial profile within Arabian lineages as a favored traits and potentially manage its extreme forms as a likely genetic disease.
Copyright © 2023. Published by Elsevier Inc.
Publication Date: 2023-12-07 PubMed ID: 38070586DOI: 10.1016/j.jevs.2023.104980Google Scholar: Lookup
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Summary
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The research article aims to provide a quantitative analysis of the variations in the shape of horse faces across different breeds, with a particular focus on Arabian horses. It employs geometric morphometrics to systematically characterize these features, which have traditionally been categorically but inadequately described as ‘dished,’ ‘straight,’ or ‘roman-nosed.’
Methodology
- The researchers took lateral profile photos of the horses and marked significant landmarks on each picture. The main focus was the dorsal curvature of the rostrum or the top part of the horse’s nose.
- These digitized points were then subjected to Generalized Procrustes Analysis. This statistical method is used to extract independent variables for size and shape, minimizing the impact of rotation and scaling alignment.
- Using these variables, the research team compared the face shapes across different breeds and within Arabian horses.
Results
- The horse breeds varied considerably in the nasal curvature, ranging from ‘extremely concave’ to ‘extremely convex.’
- More than 70% of the studied breeds had intermediate nasal concavity, classified as a straight profile.
- Arabian horses displayed the highest diversity in their face profiles, subdividing them into three distinct shape sub-groups: one dished and two straight profiles clusters.
Implications
- The findings could contribute to future genetic studies focusing on the facial profiles of Arabian horses as preferred traits. These studies can associate specific genetic markers with the observed face shapes, potentially revealing the genes responsible for these traits.
- Identifying the genetic determinants of extreme forms of face shapes may help manage health issues linked with these forms.
- The quantitative phenotyping method used in this study offers a more accurate way to represent the wide spectrum of horse face shapes, thus overcoming the limitations of the traditional categorical descriptions.
Cite This Article
APA
Alhaddad H, Powell BB, Pinto LD, Sutter N, Brooks SA, Alhajeri BH.
(2023).
Geometric morphometrics of face profile across horse breeds and within Arabian horses: Horse face geometric morphometrics.
J Equine Vet Sci, 104980.
https://doi.org/10.1016/j.jevs.2023.104980 Publication
Researcher Affiliations
- Department of Biological Sciences, Kuwait University, Shadadiya, Kuwait. Electronic address: hassan.alhaddad@ku.edu.kw.
- Department of Animal Science, UF Genetics Institute, University of Florida, Gainesville, Florida, USA.
- Biology Department, La Sierra University, Riverside, California, USA.
- Biology Department, La Sierra University, Riverside, California, USA.
- Department of Animal Science, UF Genetics Institute, University of Florida, Gainesville, Florida, USA.
- Department of Biological Sciences, Kuwait University, Shadadiya, Kuwait. Electronic address: bader.alhajeri@ku.edu.kw.
Conflict of Interest Statement
Declaration of Competing Interest The authors declare no conflict of interest.
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