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Journal of Dairy Science Vol. 65 No. 8 1562-1577
© 1982 by American Dairy Science Association ®
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Days-Open Adjusted, Annualized, and Fat-Corrected Yields as Alternatives to Mature-Equivalent Records1

J. R. Thompson2, A. E. Freeman and P. J. Berger

Department of Animal Science, Iowa State University, Ames 50011

ABSTRACT

Models for developing adjustment factors for days open, effects of alternative methods to evaluate lactation yields, and effects of alternative methods of measuring yield on sire evaluation weve investigated. Effects of days open on production were reduced by including summit production (average of 2 highest of first 3 test days) in models; however, adjustment of records by factors from models including summit production were not satisfactory for records with greater than 180 days open. Annualized yield ([total lactation production divided by days between calvings] 365) overcompensated for days open greater than 180. Days open adjusted. annualized yield, and fatcorrected yield were closely correlated. Mature-equivalent production in first parity was most predictive for yield in second parity, but yield adjusted for days open was more predictive of total comulative yield at 26, 39, and 59 mo.

Rank correlations among sire transmitting abilities computed from alternative measures were more than .86. Evaluations by yield adjusted for days open were most similar and fat-corrected yield least similar to evaluation by mature equivalent production. Changes in culling decisions and sire evaluation from use of annualized yield or yield adjusted for days open versus mature equivalent were small, and yield adjusted for days open isf preferred over annualized yield.

FOOTNOTES

1 Journal Paper No. J-10377 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 1053.

2 Department of Animal Science, University of California, Davis 95616.






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Copyright © 1982 by the American Dairy Science Association ®.