Genetic and genomic relationships among Canadian Holstein dairy cattle population and international Holstein bulls

Authors

  • Bayode O. Makanjuola Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada https://orcid.org/0000-0002-3485-0201
  • Christiana Obari Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada
  • Gabriella Condello
  • Filippo Miglior Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada, Lactanet, Guelph, Ontario, Canada https://orcid.org/0000-0003-2345-8842
  • Christian Maltecca North Carolina State University, Department of Animal Science and Genetics Program, Raleigh, North Carolina, USA https://orcid.org/0000-0002-9996-4680
  • John B. Cole Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada, North Carolina State University, Department of Animal Science and Genetics Program, Raleigh, North Carolina, USA, Council on Dairy Cattle Breeding, Bowie, Maryland, USA, Department of Animal Sciences, Donald Henry Barron Reproductive and Perinatal Biology Research Program, and the Genetics Institute, University of Florida, Gainesville, USA
  • Flavio S. Schenkel Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada https://orcid.org/0000-0001-8700-0633
  • Christine F. Baes Centre for Genomic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada https://orcid.org/0000-0001-6614-8890

Abstract

The increasing level of inbreeding in dairy cattle populations can be a concern for researchers, producers, and artificial insemination (AI) companies. High inbreeding levels can lead to the accumulation of deleterious recessive variants, depression of the mean value of economically important traits, and a reduction in available genetic diversity in the population. Advancements in reproductive technologies and the integration of genomic information into genetic evaluations have contributed to rising inbreeding levels. Given the global interest in inbreeding, there is a need to monitor inbreeding trends and develop strategies to manage its adverse effects while ensuring continued genetic progress. The objective of this study was to measure the current trends in genetic and genomic relationships among Canadian Holstein cows and international Holstein bulls. Pedigree and genotype data were provided by Lactanet Canada (Guelph, ON). Genotype information was available for 168,995 animals, for which a pedigree of 616,258 animals was extracted. Among genotyped animals, 8,491 bulls were born between 2000 and 2023, and 131,139 cows were born between 2010 and 2024. The average pedigree completeness index of all genotyped animals was greater than 99%, with a maximum pedigree depth of 30 generations. Genetic relationship values were estimated using pedigree data (R-value) and genomic data (GR-value). R-value and GR-value represent the expected and realized percentage of shared DNA between an animal and a defined reference population, respectively. This was done by iteratively tracing back the gene contribution of an animal to the reference population. In this study, the reference population was defined as currently active cows and heifers enrolled in milk recording without a documented left-herd date on the latest test day in April 2024. Results show a yearly increase in relationship within the reference and bull populations. The average genetic relationship between bulls and the reference population ranged from 9.3% to 26.5% (R-value) and from 12.9% to 40.8% (GR-value). Among bulls, those with United States registration codes had the highest relationship value with active Canadian cows and heifers, with R-value and GR-value estimates of 20.8% and 30.4%, respectively. Conversely, bulls registered in the Czech Republic had the lowest average relationship values, with R-value and GR-value estimates of 17.1% and 24.3%, respectively. Selecting sires with low average relationship values among defined reference populations as a mating strategy could reduce or maintain inbreeding at acceptable levels while preserving genetic diversity.

 

Key words: Genetic relationship, inbreeding diversity, Holstein, dairy cattle

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Published

2025-11-17

Issue

No. 61 (2025): Proceedings of the 2025 Interbull Meeting

Section

Articles

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