Impact of Culling on Modified Contemporary Comparison Sire Evaluations

Open Access
Publisher Website
Google Scholar
Abstract
Sire evaluations by modified contemporary comparison routinely are calculated separately for 1st and later lactations. The published proofs, based on all lactations are a function of information from these 2 evaluations. Four data sets from daughters of 200 widely used Holstein sires were used to examine the impact of selection of modified contemporary comparisons. Set 1 contained over 670,000 daughters with 1st and 2nd records in the herd where the 1st was initiated. Sets 2-4 contained these same 1st records but only 2nd records from the best 90, 80 and 70% of daughters based on modified contemporary deviations for milk in 1st lactation. Means for predicted difference milk based on 2nd records increased from 367 to 476, 573 and 670 kg as elimination of 2nd records increased from none to 10, 20 and 30% with corresponding SD of 274, 250, 238 and 228 kg. Correlations between predicted difference milk from 1st and 2nd lactations declined as culling as culling intensity increased (0.85, 0.81, 0.77 and 0.7) and zero, 10, 20 and 30% culling of seconds. Regression of 2nd lactation milk proof on 1st declined with increased culling (0.87, 0.75, 0.68 and 0.62). Adjustment for selection of 2nd lactation proofs from files subjected to culling produced means and SD similar to 2nd lactation proofs from files where all daughters had a 2nd record (mean = 367, 359, 359 and 360 kg, SD 274, 273, 272 and 272 kg, respectively). Adjusted 2nd lactation evaluations from culled data sets produced sire ranks nearly identical to those from unculled records.