Genetic Base Change 2010
Expected Base Changes for US Dairy Breeds in January 2010
Dr. Kent Weigel
University of Wisconsin
Every five years, genetic evaluations of US dairy cattle undergo a "base change". This is
a simple adjustment of the predicted transmitting abilities (PTAs) of bulls, cows, heifers,
and calves for the genetic progress that has been made during the most recent five-year period.
At present the "reference animals" for each breed are sire-identified cows that were born in
the year 2000. These animals have average PTAs of zero for every trait, with the exception
of somatic cell score, calving ease, and stillbirth rate, which are centered at breed average
rather than zero. In January 2010 the reference group will become sire-identified cows that
were born in the year 2005. It is important to note that the relative rankings of animals will
not change - the base change merely an exercise that keeps PTAs from getting larger and larger
each year. However, it is interesting to look at the magnitude and direction of the base change
for each trait, as this reflects the progress that we have made in our genetic selection programs
during the most recent five-year period. The expected base change for each trait, according to
the USDA-ARS Animal Improvement Programs Laboratory and the dairy cattle breed associations,
is found at the following link: http://aipl.arsusda.gov/reference/base2010.htm.
These values will be subtracted from the PTAs for each trait in January 2010.
September 29, 2009