April 2020: Genetic Base Change

Council on Dairy Cattle Breeding

The base for U.S. genetic evaluations will be updated, effective with the April 7, 2020, triannual evaluations.

The genetic bases to which (most) dairy traits are expressed in the United States have been updated every five years since 1980.

For the last base change in 2015, the average predicted transmitting abilities (PTA) of cows born in 2010 were set to zero. Milking cows born in 2015 define the new base, and their PTAs will be set back to zero with the April evaluations.

Because gains were made across five years for most traits, most PTAs will be lowered by the amount shown in Table 1 in the complete article (click here). A note of caution, Table 1 does not reflect the precise changes coming because all will be recalculated before the April 2020 run using more complete and current data.

Key points on genetic progress over the past five years:

  • Favorable gains are shown for 81 of the 102 traits (excluding conformation), while 18 were unfavorable.
  • The most important traits (all lifetime merit indexes) showed genetic improvement for all the breeds; the largest gains were for Holsteins, Jerseys and Ayrshires.
  • Genetic gains were made in all three yield traits (milk, fat, protein) for all breeds. Gains were particularly impressive for Holsteins and Jerseys.
  • Unfortunately, 13 of the 18 fertility estimates showed unfavorable changes over the five years; only Holsteins improved for all three traits.
  • Resistance against diseases in Holsteins improved for five of the six traits.
  • PTAs increased for 80 of the 90 breed conformation traits, which indicates that selection has been for the higher scores. The 10 traits with PTAs that did not increase were ones that had an intermediate optimum.



Detailed data can be found in these tables in the complete article:

  • Table 1. Difference in predicted transmitting abilities (PTAs) of cows born in 2015 compared to those born in 2010.  PTAs will decrease by these amounts to implement the 2020 genetic base change1.
  • Table 2. Differences in actual (phenotypic) performance between cows born in 2015 and those born in 2010 attributed to genetic (BV=breeding value1) and environmental changes.
  • Table 3. Relative size in percentage of the 2020 genetic base changescompared to the base changes five years earlier (2015).
  • Table 4. Percentage of the change in phenotype attributed to genetics for cows born in 2015 compared to those born in 2010 for traits with published evaluations initiated before 20101.
  • Table 5. Ratio of trait SD for base cows born in 2015 vs. those in 2010. The PTAs will be expanded (or contracted) by these ratios.
  • Table 6. Ratio of trait SD for base cows born in 2015 compared to Holsteins. The PTAs will be expanded (or contracted) by these ratios.

Impact of Genomics
The genomic revolution initiated in 2008 brought an increase in the rate of genetic improvement, primarily due to a reduction in the generation interval. A small portion of genomic benefits would have been revealed in the previous base change for cows born in 2010, but the current update will reflect all benefits from genomics achieved from 2010 to 2015.

The Bottom Line
Advocates for improving sustainability and eliminating world hunger should be amazed to see the changes in productivity in U.S. dairy. Greenhouse gases are being reduced per unit of product because of greater production per animal. We are seeing significant improvements in the animals’ appearance and health as well.

Since we’re approaching another base change, this may be a good time to remind dairy producers to adopt genetic selection strategies that could virtually eliminate any complacency of decisions between base changes. For example, if selection is based on standards like percentiles (recalculated every run) or by simply selecting the top-ranked bulls on an economic index of their choice, forward progress would occur, devoid of any delays.

Read the complete article here.




The Council on Dairy Cattle Breeding (CDCB) is a non-profit organization which in 2015 assumed the service responsibilities for calculating and distributing the genetic evaluations and genomic predictions, for managing data storage, and for analyzing and distributing dairy cattle data. These tasks were previously performed by the United States Department of Agriculture – Agricultural Research Service – Animal Genomics and Improvement Laboratory (USDA-ARS-AGIL). The Council is a partnership among AI, DHI and breed organizations. Its offices are in Bowie, Md., and more information can be found at http://www.uscdcb.com

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