Effects of culling on sire evaluations by mixed models.

The data consisted of the first two records for milk and fat yield of 677,800 daughters of 200 widely used Holstein sires. From these data, 10, 20, and 30% of second records were eliminated for least yield of milk in first lactation. Best Linear Unbiased Prediction evaluations of sires were obtained separately for both records and seconds only for culled and unculled groups and for all first records. Evaluations from second records were affected by culling with standard deviations for milk evaluations declining 58 kg as elimination of second records increased from 0 to 30%. Correlations between first and second milk evaluations declined from .84 to .70 as culling increased. Evaluations by both records showed little effect of culling with standard deviations declining only slightly with culling, and correlations among the evaluations close to unity. Adjustment of second evaluations for selection appeared to remove much effect of selection. Best Linear Unbiased Prediction evaluations and those based on the same daughters from Modified Contemporary Comparison procedures showed similar effects of culling and adjustment for culling and ranked bulls nearly identically.