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 Società Italiana per il Progresso della Zootecnica, Sept. 29 - Oct. 1, 1997, Milan, Italy.