First Lactation Contemporary Comparisons as Indicators of Environmental Influences on Daughter Records Used for Sire Evaluation

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Abstract
The accuracy of various measures of a dairy sire''s transmitting ability, using ten contemporary averages, was studied. First lactation and the mean of two or more lactation records made by artificially bred daughters of Holstein sires were adjusted for differences in herd opportunity, using first and all lactation running season contemporary averages. Adjustments were made on 4,855 cow records and the relative effectiveness of the adjustments evaluated. The first lactation con temporary averages were most effective in removing herd variance, but resulted in an increase in the herd by sire variance component estimates. The measure using all lactation records from daughters and contemporaries yielded the largest expected correlation (.93) between the mean of 100 daughters and all future daughters. Selection biases were studied between all lactation and first lactation contemporary records. Results indicated that all lactation contemporaries overestimated the environmental situation for first lactation records by 258 lb of milk.