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이광전(K . J . Lee),박경도(K . D . Park),강민식(M . S . Kang),강민구(M . G . Kang),이연근(Y . K . Lee),조광현(K . H . Cho),최재봉(J . B . Choi) 한국축산학회 1993 한국축산학회지 Vol.35 No.6
This study was undertaken to identify the changes of variance components for herd production levels of milk. Milk records were divided into low, medium, and high groups by average herd production, average herd-year production, herd standard deviation, and herd-year standard deviation. Herd standard deviations increased with average herd productions. Correlation between average herd production and herd standard deviation was 0.41, while correlation between average herd-year production and herd-year standard deviation was 0.47. Residual variance components of higher production increased remarkably, while genetic variance components of high group by herd-year standard deviation showed the same increasing trend. When records are transformed to logarithms, however, residual components of variance didn`t show the increasing trend, and the changing ratio decreased markedly without homogeneous variance components. In order to account for the heterogeneity of milk among herds, the optimum classifying criterion was an average herd-year production level. Estimates of heritabilities for low, medium and high groups were 0.185, 0.237, and 0.283, respectively. These results remarkably showed the heterogeneity of milk among dairy herds.
이광전(K . J . Lee),박경도(K . D . Park),양영목(Y . M . Yang),최윤석(Y . S . Choi),이연근(Y . K . Lee),조광현(K . H . Jo) 한국축산학회 1993 한국축산학회지 Vol.35 No.6
The results obtained from a total to 1993 milk records ranging 1985 to 1991 were as follows. 1. Milk yields and standard deviations of three production levels on the basis of ME milk yield of all cows freshening in the same herd-year were 7,284.68㎏∼9,333.28㎏and 1,370.30∼1,686.56, respectively, and therefore showed the heterogeneity among three production levels of milk. 2. When milk records were transformed to logarithms, average milk yields, standard deviations, and coefficients of variation for production levels were stable. 3. In case of transforming to logarithms, residual variance component of low group increased markedly and this result indicated that the ranks of genetic evaluations for bull-sires and bull-dams could be reversed. 4. REML estimates of heritability for low, medium, and high groups were 0.189, 0.234, 0.254, respectively, and multiple traits evaluation was necessary. 5. Proportions of sires selected from groups by herd-year production levels corresponding to top 5% based on PTAM were 18.2%, 36.4%, 45.5%, for low, medium, and high groups. 6. In case of log transformation, proportions of sires selected from groups corresponding to top 5% of PTAM were 38.9%, 61.1%, 0.0% for low, medium, and high groups, respectively. On the other hand, proportions of elite cows corresponding to top 1% were 45.5%, 54.54%, 0.0% for low, medium, and high groups. 7. Genetic correlations and rank correlations of PTAMs among low, medium, and high groups showed large values. These high correlations indicated that heterogeneity among dairy herds in Korea was due to environmental causes. 8. Without accounting for heterogeneity of milk yields among dairy herds in Korea, the direct application of evaluation models developed by advanced countries could bring the possibility of misranking genetically superior bulls and cows.