title: Changes in genetic selection differentials and generation intervals in US Holstein dairy cattle as a result of genomic selection.
abstract: Seven years after the introduction of genomic selection in the United States, it is now possible to evaluate the impact of this technology on the population. Selection differential(s) (SD) and generation interval(s) (GI) were characterized in a four-path selection model that included sire(s) of bulls (SB), sire(s) of cows (SC), dam(s) of bulls (DB), and dam(s) of cows (DC). Changes in SD over time were estimated for milk, fat, and protein yield; somatic cell score (SCS); productive life (PL); and daughter pregnancy rate (DPR) for the Holstein breed. In the period following implementation of genomic selection, dramatic reductions were seen in GI, especially the SB and SC paths. The SB GI reduced from ∼7 y to less than 2.5 y, and the DB GI fell from about 4 y to nearly 2.5 y. SD were relatively stable for yield traits, although modest gains were noted in recent years. The most dramatic response to genomic selection was observed for the lowly heritable traits DPR, PL, and SCS. Genetic trends changed from close to zero to large and favorable, resulting in rapid genetic improvement in fertility, lifespan, and health in a breed where these traits eroded over time. These results clearly demonstrate the positive impact of genomic selection in US dairy cattle, even though this technology has only been in use for a short time. Based on the four-path selection model, rates of genetic gain per year increased from ∼50-100% for yield traits and from threefold to fourfold for lowly heritable traits.
authors.affiliation: Centro Nacional de Investigación Disciplinaria en Fisiología y Mejoramiento Animal, Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias, Ajuchitlán, Querétaro, 76280, México; Animal Genomics and Improvement Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705.
authors.forename: Adriana
authors.initials: A
authors.lastname: García-Ruiz
authors.affiliation: Animal Genomics and Improvement Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705.
authors.forename: John B
authors.initials: JB
authors.lastname: Cole
authors.affiliation: Animal Genomics and Improvement Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705.
authors.forename: Paul M
authors.initials: PM
authors.lastname: VanRaden
authors.affiliation: Animal Genomics and Improvement Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705.
authors.forename: George R
authors.initials: GR
authors.lastname: Wiggans
authors.affiliation: Centro Nacional de Investigación Disciplinaria en Fisiología y Mejoramiento Animal, Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias, Ajuchitlán, Querétaro, 76280, México;
authors.forename: Felipe J
authors.initials: FJ
authors.lastname: Ruiz-López
authors.affiliation: Animal Genomics and Improvement Laboratory, Agricultural Research Service, US Department of Agriculture, Beltsville, MD 20705 curt.vantassell@ars.usda.gov.
authors.forename: Curtis P
authors.initials: CP
authors.lastname: Van Tassell
mesh_terms: D000818:Animals; D002417:Cattle / Q000235:genetics*; D003612:Dairying / Q000706:statistics & numerical data; D005260:Female; D008297:Male; D008892:Milk / Q000706:statistics & numerical data; D012641:Selection, Genetic
keywords: Holstein; dairy cattle; generation interval; genetic improvement; genomic selection