RECORDS CONTRIBUTING TO NATIONAL GENETIC EVALUATIONS BY YEAR, REGISTRATION STATUS, HERD SIZE, AND REGION

Lactation records from official DHIA were screened for usability in co mputing USDA-DHIA genetic evaluations. Counts of usable lactation reco rds by state, registration status, and year were examined. Number of c ows enrolled in official record-keeping plans of DHIA was the denomina tor for calculation of percentage of official DHIA records usable in g enetic evaluations for state-years. Percentage of official records usa ble 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 decli ne from 64% of all usable records during 1968 to only 42% during 1990. Effects of year, DHIA region, average herd size, and average percenta ge of registered cows were important for explaining variation in perce ntage of records usable for genetic evaluations for state-years. State s with large average herd sizes and low percentages of dairy cows that were registered had low percentages of records usable for genetic eva luations. Increased official DHIA participation and improved sire iden tification increases the percentage of records usable for genetic eval uations and helps facilitate genetic improvement.