Genetic Gains in Lifetime Merit Indexes during the use of three Genetic Evaluation Methods

Abstract

Genetic evaluation procedures available and adopted by U.S. dairy producers have had a positive impact on genetic improvement for a multitude of traits. The objective of this research was to compare the progress in several traits during the use of six evaluation methods. Five additional genetic evaluation procedures were produced by USDA following the daughter-dam comparison initiated in 1915. These included two herdmate comparisons (versions implemented in 1962 and 1968), Modified Contemporary Comparison (MCC, Nov. 1974), Animal Model Evaluation (AME, July 1989), and Genomic Evaluation (GE, Jan. 2009). The MCC was largely based on combining (weighting) information by the inverse of the expected variance of each effect in the model. The AME  was assumed to have best linear unbiased prediction properties while including primarily the same effects as the MCC. About two years generally elapses before the results are evident in the milking population as nine months are necessary before their first offspring are born, then more time is required before most of inseminations are based on the new evaluations. Average Estimated Breeding Values (EBV) were derived within each of the evaluation periods. The contribution of several additional traits contributing to the overall gains was derived. The transition to each subsequent evaluation brought increases in the genetic gains with one exception. The reason for the declines in annual genetic gains using AME following MCC remains unresolved. The GE is currently generating higher gains in lifetime merit indexes than the earlier methods, and in the four, Holstein composites gains exceeded twice that from the AME method. Genetic economic gains averaging $51 to $67 per year were evident across the 42-years examined.