Submitted to: AIPL Research Reports
Publication Type: Government Publication
Publication Acceptance Date: July 18, 1996
Publication Date: N/A
Interpretive Summary: Changes in USDA-DHIA genetic evaluations in July 1996 were documented so that the dairy industry could make most effective use of information that incorporates improvements in methodology and to address industry concerns over decreases in bull evaluations in January 1996. New lactation weights were based on numbers of test days and samples instead of lactation length because the numbers of supervised test days, other test days, supervised samples, and other samples provide further information about accuracy of the record. The main change for July was reduced weighting for less frequent testing. To coordinate release of national and international evaluations, the schedule for USDA-DHIA evaluations in 1997 will be changed so that national evaluations will be released in February and August instead of in January and July. In response to industry questions about January 1996 evaluations, researchers investigated minor technical changes in computer programs, reduced variation in evaluations, and reduced genetic trend. Animals of the same generation in the same country evaluated at the same time were found to be compared the most accurately. Understanding by dairy producers of improvements in genetic evaluation methodology promotes appropriate use of information released to the industry and advances genetic progress.
Technical Abstract: Changes in USDA-DHIA genetic evaluations in July 1996 were documented. New lactation weights were calculated from record-standards variables. Instead of lactation length, weights for new records are now based on numbers of test days and samples. The main change for July was reduced weighting for less frequent testing. The new weights are used only if the new weight is less than or equal to the previous weight based on lactation length. The evaluations on a U.S. basis released by the International Bull Evaluation Service (INTERBULL) in August 1996 are official for any bull that does not have a USDA-DHIA evaluation. To coordinate release of national and international evaluations, the schedule for USDA-DHIA evaluations in 1997 will be changed (subject to approval by the Council on Dairy Cattle Breeding) so that national evaluations will be released on or about February 10 and August 11. Because evaluations in January 1996 were slightly lower for many bulls of interest and the standard deviation (SD) of evaluations was about 2.5% smaller, researchers investigated: 1) minor technical changes in animal model programs, 2) reduced variation, and 3) reduced genetic trend. January 1996 and July 1996 versions of the computer programs produced the same SD when compared using the same data set. Although INTERBULL evaluations account for changes in variance, estimates of the reduction in U.S. SD were smaller than USDA estimates. Genetic trend for all-parity evaluations in January 1996 (although lower than for all-parity evaluations in July 1995) was higher than trend for January 1996 first- parity only evaluations. Animals of the same generation in the same country evaluated at the same time are compared the most accurately.