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Journal of Dairy Science Vol. 54 No. 7 1041-1051
© 1971 by American Dairy Science Association ®
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Biases in Dairy Sire Evaluation Attributable to Genetic Trend and Female Selection

G. L. Hargrove1 and J. E. Legates

Department of Animal Science, North Carolina State University, Raleigh 27607

ABSTRACT

Genetic trend, female selection, and proportion of cows completing a given lactation were estimated with records (305-day, 2x, mature basis) from six Southestern states. There were 251.322 Holstein and 59,274 Jersey records for calvings between October, 1964, and November, 1968. Female selection defined as the average of selected cows minus the mean of all cows was 164 kg milk for Holsteins and 161 kg for Jerseys. Genetic trend in annual milk production was 53 and 25 kg for Holsteins and Jerseys. Young sires with first progeny information just available, when compared to an older sire with progeny information for the previous eight years, may be rated lower simply as a result of female selection and genetic trend. This difference in the average of daughters minus adjusted-herd-mate average was at least 75 kg milk for Holsteins and 54 kg for Jerseys. An alternative to the present U.S. Department of Agriculture herdmate deviation was suggested, that of using only first-lactation contemporaries rather than all-lactation herdmates. Although there are approximately one-third as many contemporaries and contemporary sires as herdmates and herdmate sires, variance of adjusted deviations increased 5% or less for contemporary over herdmate deviations. Correlations of successive annual sire evaluations on contemporary or herdmate comparisons indicated either method was equally acceptable by this criterion. The contemporary method would avoid biases due to female selection, reduce computing costs, and permit clearer interpretation of sire summaries.

FOOTNOTES

1 Present address: Department of Dairy Science, Pennsylvania State University, University Park 16802.






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Copyright © 1971 by the American Dairy Science Association ®.