HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Cassell, B. G. Articles by Norman, H. D. Search for Related Content PubMed PubMed Citation Articles by Cassell, B. G. Articles by Norman, H. D.

Modified Contemporary Comparisons for First and Second Lactations in the Same and Different Herds²

Department of Animal Science, North Carolina State University, Raleigh 27650

H. D. Norman

US Department of Agriculture, Research Center, Beltsville, MD 20705

ABSTRACT

Separate sire evaluations by Modified Contemporary Comparison for first and second lactations were calculated for 200 widely used Holstein bulls from a file containing only first or second records of all daughters and from two independent subsets of the same data. Sire evaluations based on both first and second lactations also were computed. Correlations between first lactation evaluations in one independent data set and second lactation evaluations in the other were .87 and .84. First lactation evaluations accounted for only about 75% of the variation in second record evaluations, suggesting a need for some form of later record sire evaluation, at least for the selection of sires of sons. Within sire, daughter variation for first records was not useful in predicting difference between first and second record sire evaluations. Second lactation evaluations increased relative to firsts as culling increased, suggesting culling bias in Modified Contemporary Comparisons for later records. An adjustment based on an empirical regression of later records on firsts produced second evaluations with means and standard deviations nearly identical to those of first records. Correlations between first and adjusted second evaluations were .87 for both independent data sets. Difference between adjusted second and first evaluations were correlated .15 with culling, compared to .25 for unadjusted seconds. Important sire differences in first and second lactation evaluations were detected in all data sets. Such differences were unaltered by adjustment for selection.

² Paper No. 8207 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh.

¹ Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.