Ratings of equine conformation – new insights provided by shape analysis using the example of Lipizzan stallions
The quality of individual ratings of conformation traits can commonly be evaluated by calculating inter-rater correlations and repeatability coefficients. We present an approach in which we associate the individual rating scores with the underlying horse shapes derived from standardized images, perf...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-06-01
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| Series: | Archives Animal Breeding |
| Online Access: | http://www.arch-anim-breed.net/59/309/2016/aab-59-309-2016.pdf |
| Summary: | The quality of individual ratings of conformation traits can commonly be
evaluated by calculating inter-rater correlations and repeatability
coefficients. We present an approach in which we associate the individual
rating scores with the underlying horse shapes derived from standardized
images, performing a shape regression. Therefore, we analyzed the
shape of 102 Lipizzan stallions from the Spanish Riding School in Vienna,
defined by 246 shape-correlated two-dimensional coordinates using techniques
from the field of image analysis and geometric morphometrics. In addition we
examined the differences in the conformation classifiers' perceptions of type traits and functional traits. In this study part, the rating
scores of eight conformation classifiers were tested for agreement, yielding
inter-rater correlations ranging from 0.30 to 0.55 and
kappa coefficients ranging from 0.08 to 0.42. From the 12 scoring traits
assessed on a valuating scale, type traits with a mean kappa
coefficient (<i>κ</i>) of 0.27 demonstrated a higher agreement than functional traits
(<i>κ</i> = 0.14). Based on 246 two-dimensional anatomical and somatometric
landmarks, the shape variation was analyzed by the use of generalized orthogonal
least-squares Procrustes (generalized Procrustes analysis – GPA) procedures. Shape variables were regressed
into the results from visually scored linear type trait classifications
(shape regressions). From the 48 performed shape regressions (eight
classifiers, six traits), 42 % resulted in a significant equation. In
58 % of the ratings, no association between scores and the phenotype of
the horses was found. Phenotypic differences of model horses along
significant regression curves of mean ratings and individual ratings were
exemplarily visualized and compared by warped and averaged images. Finally, we
demonstrated that the method of shape regression offers the possibility to
evaluate the association of individual ratings from expert conformation
classifiers with the shapes of horses. The detected bias in classifiers'
rankings have not been considered in breeding programs, and its impact on
selection procedures still needs further research. |
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| ISSN: | 0003-9438 2363-9822 |