Selection index procedures can condense observations of daily yield into estimates of lactation yield and persistency. Condensed data instead of test day data in an animal model might provide many of the same benefits with less computation. The best prediction method uses the phenotypic covariance matrix among daily yields to compute reliabilities and covariances of estimated yield and persistency for any data pattern. The measure of persistency is uncorrelated with yield if persistency coefficients are deviated from a central point of the lactation. Recent records containing both yield and persistency data and earlier records containing just yield data could be combined easily in genetic evaluations.

P. M VanRaden

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 23: Opening: plenary; technology; transfer; beef cattle; dairy cattle; pigs., , 347–350, 1998
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