Improvement of lactation milk and persistency using the eigenvectors of the genetic covariance matrix between lactation stages |
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| Authors: | K Togashi CY Lin |
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| Institution: | aHokkaido National Agricultural Experiment Station, Hitsujigaoka 1, Toyohiraku, Sapporo, 0628555, Japan;bDairy and Swine Research and Development Centre, Agriculture and Agri-Food, Canada |
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| Abstract: | First lactation milk production of Japanese Holstein cows was partitioned into ten stages. A quartic Legendre polynomial (k = 5) under an animal model was used to estimate the additive genetic covariance matrix between these ten stages. Various selection indexes with or without restrictions were constructed using the eigenvectors of the genetic covariance matrix. These eigen indexes were designed to improve lactation milk and persistency defined as difference in milk between DIM 280 and DIM 55. Two sets of economic weights between lactation milk and persistency and three levels of restriction on the intended gains in persistency were applied. The unrestricted index based on the first three eigenvectors achieved more than 99.9% of the net merit of the unrestricted index based on the first five eigenvectors. The advantage of unrestricted index over conventional selection based on lactation EBV increases with increasing economic weight assigned to persistency. The construction of the restricted eigen index does not require economic values between lactation milk and persistency and thus is more practical than the unrestricted eigen index which requires information on the economic values of both. The index coefficients of the eigen indexes reveal the relative selection emphasis among various stages of the lactation. When the degree of restriction or economic value for persistency increases, a greater selection emphasis was placed on the later part of the lactation than on the early part in order to realize the desired persistency. The developed eigen indexes provide useful information and easy understanding of the selection practice. A numerical example was given to illustrate the construction of the restricted eigen index. |
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| Keywords: | Selection index Eigenvectors Persistency Milk yield |
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