C. Maltecca1*, F. Tiezzi1, J.B. Cole2, and C. Baes3,4
1Animal Science Department, North Carolina State University, Raleigh, 27695
2USDA, Agricultural Research Service, Animal Genomics and Improvement Laboratory, Beltsville, MD 20705-235
3Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada
4Institute of Genetics, Vetsuisse Faculty, University of Bern, Bern, Switzerland
*Corresponding author
2019 J. Dairy Sci. (?)
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The advent of genomic selection paved the way for an unprecedented acceleration in genetic progress. The increased ability to select superior individuals has been coupled with a drastic reduction in the generation interval for most dairy populations. This represents both an opportunity and a challenge. Homozygosity is now rapidly accumulating in dairy populations. Currently, inbreeding depression is managed mostly through culling at the farm level and by controlling the overall accumulation of homozygosity at the population level. A better understanding of how homozygosity and genomic load are related will guarantee continued genetic improvement while curtailing the accumulation of harmful recessives and maintain enough genetic variability to ensure the possibility of selection in the face of changing environmental conditions. In this paper we present a snapshot of the current dairy selection structure as it relates to response to selection and accumulation of homozygosity, briefly outline the main approaches currently used to manage inbreeding and overall variability, and present some approaches that can be used in the short term to control accumulation of harmful recessives while maintaining sustained selection pressure.
Key Words: genomic evaluation, inbreeding, mating