Expected Base Changes for US Dairy Breeds in January 2014
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 2005. 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 December 2014 the reference group will become sire-identified cows that were born in the year 2010. 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 Council on Dairy Cattle Breeding and the dairy cattle breed associations,is found at the following link: http://aipl.arsusda.gov/reference/base2014.htm. These values will be subtracted from the PTAs for each trait in December 2014.