Principal component analysis of linear udder type traits and their relationship with milk yield and composition in indigenous Sahiwal cattle

Abstract

Objective: The present study was aimed at i) reduction in dimensionality using principal component analysis (PCA) of 17 linear udder type traits to define those components which best represent udder and teat conformation of Indian Sahiwal cattle and ii) to identify those components having strongest relationship with milk production traits in Sahiwal cattle. Methods: The PCA included 17 linear udder type traits using the correlation matrix between the traits to ensure that all traits are standardized in the analysis. Bartlett's sphericity test was used to determine the degree of interrelations between variables and adequacy for use in factor analysis. The relationship of these principal components with milk production traits was analysed using the general linear model. Results: The means of linear udder type trait measurements varied between-2.21 for udder balance and 136.35 for udder circumference. Out of 17 principal components, six were extracted using Kaiser Rule criterion. The identified six components could explain 75.777% of the cumulative variance between the linear udder type traits. The communality ranged from 0.476 (rear udder width) to 0.967 (fore teat length) for all these 17 different udder type traits. A relation between first principal component and 305-day milk production was significant with a positive and non-significant effect of 305-day milk-fat yield and 305-day milk-protein yield. Conclusion: Results of PCA suggest that the use of orthogonal synthetic variables principal component one (PC1), two (PC2), and three (PC3) provided a means of reduction in the number of linear udder type traits to be recorded in Sahiwal cattle which could be used in explaining the whole udder and teat conformation. The PC1 can be used in selection to explain the mammary system of better milk producing animals to be used in breeding programmes.