Abstract
Test-day lactation records of primiparous Holstein cows over an eleven-year period were evaluated for persistency and estimates of its heritability and correlation with other lactation traits computed. In this study, 435390 test day records of the first lactation Holstein cows that calved between 2001 and 2011 from 659 herds were analyzed using various procedures of SAS. Per1% (dividing total milk yield between 101-200 days by the yield of the first 100 days of lactation) measure was preferred in the selection of animals for milk yield persistency because of higher heritability (0.084 ± 0.009) and the lower phenotypic correlation with 305 days milk yield (0.424) compare to other persistency measures. The result showed that cows which calved during summer and autumn had slightly higher persistency in comparison to cows that calved in spring or winter. The persistency can be affected by the age at first calving, as cows that calved at a younger age had lower persistency.
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