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Journal of Dairy Science Vol. 50 No. 9 1458-1467
© 1967 by American Dairy Science Association ®
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Usefulness of Part Records to Estimate the Breeding Values of Dairy Cattle1

R. C. Lamb2 and L. D. McGilliard

Department of Dairy, Michigan State University, East Lansing

ABSTRACT

Complete lactations for 24,602 Holsteins were used to measure heritabilities and repeatabilities of monthly and cumulative production, to obtain genetic and pheno-typic correlations between part and whole records, and to measure the relative genetic gain in whole records from selection on part records.

Repeatabilities were largest in the center months and increased with added months of cumulative production. Heritabilities of milk for parts increased gradually through the first lactation but for all lactations varied around .10 increasing to .16. Genetic correlations between monthly and total production were generally .9 or larger and were largest for the center of the lactation.

Phenotypic correlations of monthly with total production in the same or subsequent lactations were largest in months 4 to 6. Adding a second month to the first contributed the largest increase in accuracy of predicting that complete lactation, and the correlation exceeded .9 by the time the fifth month was added. A succeeding lactation could be predicted nearly as accurately by a part of the first lactation as by the whole first.

Selection on production for a single month will provide less genetic progress than selecting on the complete record, but cumulating parts should increase relative efficiency with each added month.

FOOTNOTES

1 Journal Article no. 4204. Michigan Agricultural Experiment Station.

2 Present address: Dairy Cattle Research Branch, ARS, USDA, Department of Dairy Science, Utah State University, Logan.






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Copyright © 1967 by the American Dairy Science Association ®.