Records contributing to national genetic evaluations by year, registration status, herd size, and region.

Lactation records from official DHIA were screened for usability in computing USDA-DHIA genetic evaluations. Counts of usable lactation records by state, registration status, and year were examined. Number of cows enrolled in official record-keeping plans of DHIA was the denominator for calculation of percentage of official DHIA records usable in genetic evaluations for state-years. Percentage of official records usable for genetic evaluations had a small increase from 44% during 1968 to 49% during 1978, had a steep increase through 1988 (65%), and then showed little change during the last 2 yr. Number of usable records of registered cows for genetic evaluations increased from 604,570 during 1968 to 864,630 during 1990, which, nevertheless, represented a decline from 64% of all usable records during 1968 to only 42% during 1990. Effects of year, DHIA region, average herd size, and average percentage of registered cows were important for explaining variation in percentage of records usable for genetic evaluations for state-years. States with large average herd sizes and low percentages of dairy cows that were registered had low percentages of records usable for genetic evaluations. Increased official DHIA participation and improved sire identification increases the percentage of records usable for genetic evaluations and helps facilitate genetic improvement.