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Analysis of Records Expressed as Deviations¹

Department of Animal Science, North Carolina State Universityat Raleigh

ABSTRACT

Many analyses of dairy records expressed as deviations from various herdmate averages are made, yet many problems encountered in such analyses have not been investigated. Van Vleck et al. (2) studied some of the situations arising from the use of different types of herdmate averages, and showed that unbiased estimates of genetic components could be obtained from a one-way classification when certain simplifying assumptions were made. The purpose of the present study was to investigate the magnitude of the bias arising from the assumption that each herdmate was by a different sire, and to extend the derivation to the expectations of variance components in a two-line hierarchial analysis of variance.

The data used were the 305-day, 2x, M.E. milk yields, and actual fat percentages of 3,092 lactations of 1,560 cows in nine North Carolina Holstein herds. Analyses were conducted independently for first and all lactations. Each lactation was expressed as a deviation from the average of paternally unrelated animals having records in the same herd-year-season subclass (herdmates).

¹ Published with the approval of the Director of Research, North Carolina Agricultural Experiment Station. The computing services for this investigation were provided by NIH Grant No. FR-00011.