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Genetic And Environmental Factors In Dairy Sire Evaluation. I. Effects Of Herds, Months, And Year-Seasons On Variance Among Lactation Records; Repeatability And Heritability



Genetic And Environmental Factors In Dairy Sire Evaluation. I. Effects Of Herds, Months, And Year-Seasons On Variance Among Lactation Records; Repeatability And Heritability



Journal of Dairy Science 48: 347-351



More than 39,000 Iowa DHIA and DHIR Holstein lactation records provided the basic data for checking some of the parameters and assumptions currently used in dairy sire evaluation procedures in the United States. The components of variance for herds were about 32% of the total variance with both milk and milk fed records but only 17% with test. The components for months were 1.4 and 1.7% of the total variance with milk and milk fat records and only slightly higher for year-seasons. However, the interactions of herds with months and year-seasons contributed 3 to 5% of the total variance. Grouping of records according to either rolling year-season or fixed year-seasons was about equally suitable as a means of removing year-season variance with deviation records. However, the pooling of records from more than one year into season averages was less effective, because significant year-season variance remained in the deviations. Repeatabilities of records expressed as deviations from herd-year-season averages were .50, .47, and .72 for milk, milk fat, and test, respectively. Heritabilities, estimated as twice the regression of daughter or dam, within herd-year-seasons, were .22, . 18, .53 for milk, milk fat, and test.

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Accession: 014492997

Download citation: RISBibTeXText

PMID: 14292221

DOI: 10.3168/jds.s0022-0302(65)88226-1


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