Morphological structure of Zulu sheep based on principal component analysis of body measurements

Abstract

Information regarding morphology of indigenous sheep in South Africa is scant, and even where data exist it is rarely presented using standardised methodologies. Principal component analysis (PCA) was applied to 13 body measurements in order to provide an objective description of the body shape and size of 1665 Zulu sheep, obtained from rural communities of KwaZulu Natal. Data was analysed separate for young (no permanent incisors) and adult sheep (≥2 pairs of permanent incisors). On average mature males measured higher than mature ewes in most morphometric traits. The correlation coefficients between different body measurements in young sheep were all significant except for correlation between ear length and tail length whilst in adult sheep 79 out of 96 combinations showed significant correlation. Body weight and heart girth had the highest correlations in both age groups. Ear length and tail length related combinations had lower correlation coefficients in both age groups. The PCA of morphometric traits extracted two components with a total variance of 66.85% in young sheep and four components in adult sheep which explained a total variance of 62.13%. The first factor (PC1) in each case had high loadings for variables relating to body size, whilst PC2 had high association with traits reflecting body shape. The PC3 had high factor loadings for head length and head width, and thus defined head size. Tail length, ear length and whither height on the other hand contributed least towards total variation. The use of principal components was more appropriate than the use of original correlated variables in predicting body weight of Zulu sheep. PCA was able to identify traits with greater variability, these can be improved with greater success in breeding programmes and also the number of variables was reduced to give a concise picture of morphological structure (body size and shape) of a Zulu sheep. These components can as well be used in predicting body weight of Zulu sheep