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Journal of Dairy Science Vol. 58 No. 1 116-121
© 1975 by American Dairy Science Association ®
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Relations Between Sire Summaries of First and Second Lactations1,2,

M. A. Tomaszewski, B. T. McDaniel, H. D. Norman and F. N. Dickinson

Department of Animal Science, North Carolina State University at Raleigh, Raleigh 27607
Animal Physiology and Genetics Institute, U.S. Department of Agriculture, Beltsville, Maryland 20705

ABSTRACT

Sire summaries of one or more progeny in first lactations in each of 20 or more herds were compared to progeny in second lactations of the same 133 Holstein bulls. Progeny in second lactations were also in 20 or more herds, but these herds were completely different from those having first lactation progeny. Since it is unlikely that any of the progeny were common to both the first and second lactation summaries, associations between summaries should estimate genetic associations. Progeny were compared to either contemporaries in first or second lactation or herdmates of all ages. Correlations between summaries for first and second lactations for deviations of milk yield ranged from .56 to .62 compared to an expected correlation for deviations from herdmates of .66. Correlations were highest when progeny were deviated from herdmates of all ages. A progeny test on first lactation milk is about 85% as accurate in predicting second lactation performance as a progeny test on second lactations. Progeny tests for milk yield from only progeny in first lactation are sufficient for most objectives of selection.

FOOTNOTES

1 Paper number 4353 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC.

2 Supported in part by United States Department of Agriculture, Animal Physiology and Genetics Institute Contract USDA-ARS 12-14-100-11,345 (44).






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Copyright © 1975 by the American Dairy Science Association ®.