GENETIC EVALUATIONS IN THE UNITED STATES: PRESENT METHOD AND PROPOSED CHANGES

Wiggans G.R.

Animal Improvement Programs Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, Maryland, USA

Key words: Genetic evaluation, animal model, test-day model

Genetic evaluations in the United States currently are computed with a state-of-the-art animal model, which contributes to a rapid rate of genetic progress. This model, which was implemented in 1989, enables information from all relatives of each cow with lactation records to contribute to her evaluation and that of her sire. Unknown-parent genetic groups are defined to allow recognition of the improvement in genetic level over time and the differences between unknown sires and dams. Records from the first five lactations are included using a repeatability model. A first lactation is required for a record to affect evaluations of relatives. Advances in computer technology and evaluation methodology have allowed improvements to the US evaluation system since 1989 to include (1) use of records from later herds for cows that change herds, (2) accounting for reduced genetic variance of projected records, (3) adjustment for heterogeneous variance, (4) inclusion of age and parity in the model as well as the use of multiplicative preadjustments, (5) accounting for inbreeding when forming the inverse of the relationship matrix, (6) incorporation of Canadian evaluations, (7) calculation of evaluations for productive life and somatic cell score, and (8) inclusion of unsupervised records subject to additional editing. Evaluations are distributed widely, primarily through industry cooperators and the internet. A test-day model is planned so that environmental influences can be estimated more accurately by defining the effect of environment on a test-day basis. Test-day data have been collected for calvings since 1990. A within-herd analysis is used to estimate test-day effects and herd-specific age and season effects. The genetic evaluation model accounts for genetic differences in the shape of the lactation curve and the rate of maturity by an across-herd multitrait analysis. Lactation data before 1990 are included through correlations with test-day traits. Individual genetic estimates by stage of lactation and parity allow greater precision in definition of genetic indexes. Implementation of a test-day model for US evaluations is anticipated by the year 2000.

FROM: 32nd Inter. Symp., "Animal Production: Advances in Technology, Accuracy and Management," 50th Anniversary SocietÓ Italiana per il Progresso della Zootecnica, Sept. 29 - Oct. 1, 1997, Milan, Italy.