Principal component analysis of the exterior traits in dairy cows
The present study was undertaken to study the relationship between different body measurements and to develop unobservable factors (latent) to define which of these measurements best represent body conformation in the dairy cows. Biometrical observations were recorded on 109 Red Steppe dairy cows randomly selected from State Enterprise «Breeding reproducer «Stepove» (Mykolayiv region, Ukraine) during the 2001–2014. Principal Component Analysis (PCA) was used to account for the maximum portion of variation present in the original set of variables (body traits in cow) with a minimum number of composite variables through STATISTICA software. Most of the pairwise phenotypic correlations among the exterior traits in dairy cows were positive and significant. The Pearson’s correlation coefficients of the body measurements ranged from 0.215 (chest depth – cannon circumference) to 0.889 (height at withers – rump height). In factor solution of the Principal Component Analysis, two (latent) which explained 48.5% of the generalized variance were extracted. The first principal component (PC1) explained general body confirmation and explained 33.5% variation. It was represented by significant positive loading for height at withers, rump height, diagonal length from point of shoulder to pin bone, chest depth, chest circumference etc.). The second principal component (PC2) accounted for an additional 15.0% of the generalized variance and was interpreted as an indicator of body shape (e.g., endomorphic vs. ectomorphic). It was represented by significant negative loadings for height at withers, rump height, diagonal length from point of shoulder to pin bone, but significant positive loadings for chest width, chest depth, chest circumference and cannon circumference. The study also revealed that factors extracted from the present investigation could be used in breeding programs of the dairy cattle.
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