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Genetic and environmental changes in dairy traits revealed from a genetic base update.

H. D. Norman



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Genetic and environmental changes in dairy traits revealed from a genetic base update.
H. D. Norman*1, P. M. VanRaden2, J. W. D�rr1. 1Council on Dairy Cattle Breeding Bowie, MD, 2Animal Genomics and Improvement Laboratory, Agricultural Research Service, USDA Beltsville, MD.

The genetic bases to which (most) dairy traits are expressed in the United States has been updated every 5 years since 1980. For a base change, the average predicted transmitting abilities (PTA) for cows born in the designated year is subtracted from the current PTAs for all animals; i.e., it's the gain (or loss) in PTAs for animals across the 5-year period. The rationale for changing the base is to make users of genetic evaluations aware the standards set for genetic selection in the past may no longer meet the quality needed to remain competitive. Eighty-one of the 102 breed-traits for yield and fitness traits showed favorable gains. The base change for Holsteins and Jerseys will reduce PTA milk by about 223 and 238 kg., respectively. PTAs for fat and protein will be adjusted down by about 8 to 11 kg. Changes in PTAs for somatic cell score (SCS) will be small for all breeds except Holsteins (0.08). PTAs for productive life will be reduced by 0.6 to 1.9 mo for 4 breeds. Changes among breeds in fertility trait were unexpected; only Holstein improved in the 3 traits. The PTAs for cow livability improved for 3 of the 6 breeds (0.74 mo for Holsteins). Holstein resistance against diseases improved for 5 of the 6 traits. The genomic revolution initiated in 2008 increased the rate of genetic improvement, primarily due to a reduction in the generation interval. Improvement in Brown Swiss, Holsteins and Jerseys were greater for milk traits (7 to 64%) than for the previous base change. The Guernseys, Holsteins, and Jerseys showed larger gains (43 to 100%) in the lifetime merit indexes than during the previous 5-years. Results show how much of the changes in phenotypes in dairy traits that had evaluation initiated since 2008 is attributed to genetics and environment. The genetic contribution accounted for 45%, but was greater for the 3 traits with the largest emphasis in net merit dollars (averaged 69%) and for the most populous breed, Holsteins (71%). These changes in productivity should help eliminate world hunger and reduce greenhouse gas emissions from requiring fewer animals.

Keywords: genetic base, national evaluation, predicted transmitting ability.