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Journal of Dairy Science Vol. 55 No. 6 845-850
© 1972 by American Dairy Science Association ®
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Intrasire Regression of Daughter on Herdmate Performance: Nature of Estimators and Trend of Estimates

I. L. Mao1, C. R. Henderson and P. D. Miller

Department of Animal Science, Cornell University, Ithaca, New York 14850

ABSTRACT

A conventional computing formula was a consistent estimator of the intrasire regression of daughter on herdmate performance measured by adjusted herdmate average without infinite herd size. The estimator leads to another consistent estimator of the additive genetic portion of total variation among herds but subject to independence of herd environment and herd genetie structure. Nearly 900,000 milk records for all lactations of New York artificially inseminated Holstein cows from 1956 to 1968 were analyzed under the mature equivalent and the new age-month adjustment systems. Age-month adjusted records appear to have slightly lower yearly means and approximately 7.3% less variance. Mean and variance both increased with time. No significant time trends were observed for intrasire regressions, for which .9 seems suitable for all practical purposes regardless of adjustment systems and time trends. A linear regression for relative genetic variation among herds on years weighted by inverses of variances within years suggested that, with zero co-variance between herd genetie and non-genetic variates, the additive genetic variation relative to the total variation among herds has been decreasing .6% a year since 1959 for the Holstein artificial insemination population in northeastern United States.

FOOTNOTES

1 Present address: Department of Animal Science, University of Guelph, Guelph, Ontario, Canada.






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Copyright © 1972 by the American Dairy Science Association ®.