Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/12/2002
Publication Date: N/A
Technical Abstract: Genetic progress in dairy cattle is largely determined by the merit of bulls used to sire the next generation. Overall bull merit is influenced by three factors: merit of parents, accuracy of progeny test (PT), and intensity of subsequent selection. The objective of this study was to calculate the portion of PT bulls selected and selection differentials for production traits in 10 national bull populations. Data were from the routine genetic evaluation files for Holstein bulls from Interbull. The PT decisions in 1995 - 1996 were evaluated. Bulls were considered returned to service (i.e. selected) based on the addition of >= 200 daughters in the interval three years to five years after the PT decision run. Where data were available, the second appearance of a bull in Interbull results was considered the PT decision run. Otherwise, age requirements were applied. Selection differentials were computed as the differences between the mean evaluations for selected bulls and all PT bulls, divided by the sire standard deviations provided by Interbull. Proportion of bulls returned to service averaged 8% and ranged from 3 to 17% across countries. However, som bulls actually returned to service may not have had sufficient customer int to meet our definition of 200 added daughters. Selection pressure was gener highest for protein. Selection differentials for estimated breeding value m ranged from 0.53 to 1.47 standard deviation units. Corresponding values for were 0.37 to 1.15 and for protein were 0.58 to 1.61. Selection differential would be affected by selection for traits other than yield. Differences in proportion returned to service may be impacted by intensity of parental selection, number and accuracy of PT bulls sampled, and semen importation policies and export opportunities.