Stability of Evaluations of Bulls Sampled by Artificial Insemination and Other Organizations

Changes in evaluations during firstand second-crop periods were computed from up to 8 Modified Contemporary Comparison evaluations during each pe- riod for 1232 AI-and 217 non-Alsampled Holstein bulls; repeatability at last Modified Contemporary Comparison evaluation was ~.90.Evaluations were numbered consecutively within period.Effect of evaluation number within testing period on the bull's milk.or fat evaluation was estimated with a model, including fixed effect of bull in addition to evaluation number.For subsets of Aland non-AI-sampled bulls born from 1970 to 1975 and from 1976 to 1981, evaluations of both types of bulls increased from the initial first-crop evaluation and then remained fairly constant during the remainder of the first-crop period.With the inclusion of secondcrop daughters, evaluations decreased significantly more for non-AI-than for AI-sampled bulls born from 1970 to 1975 (milk, 108 vs. 28 kg; fat, 3.5 vs. 1 kg).The reduction in evaluations was larger for non-AI-sampled bulls born af- ter 1976 (milk, 184 kg; fat,7 kg) but was unchanged for AI-sampled bulls.Last seeond-crop evaluation minus the second to last first-crop evaluation (difference 1) was calculated.Expected standard deviation of change for each difference of each bull was calculated and used to stratify bulls into eight change classes.Percentages of bulls in each class were