Overview of Genetic Response Formula

Before diving into genomic selection, it’s important to revisit the genetic response formula, which defines the rate of genetic progress in dairy cattle. This formula is based on four key factors:

1. Accuracy of Genetic Evaluations: The precision with which we assess an animal’s genetic merit.
2. Selection Intensity: The rigor with which top animals are chosen for breeding.
3. Genetic Standard Deviation: The amount of genetic variation present within the population.
4. Generation Interval: The average age of parents when their offspring are born.

By optimizing these factors, dairy geneticists have achieved substantial genetic progress over the years. However, as of 2008, the industry faced two challenges: a long sire generation interval and low accuracy in female genetic evaluations.

Genomic Selection: A Game Changer

In 2008, the development of a BeadChip capable of testing approximately 50,000 SNPs (Single Nucleotide Polymorphisms) revolutionized dairy cattle genetics. SNPs are single base pair DNA mutations that can be used to generate genomic Predicted Transmitting Ability (PTA) for young animals. This advancement solved the industry’s two primary challenges:

1. Reduced Sire Generation Interval: By providing genetic information on young bulls before they are sexually mature, the sire generation interval was reduced from 6 years to 2 years.
2. Improved Female Genetic Evaluations: Females now have genetic evaluations that are nearly as accurate as those of young males, allowing for more reliable selection of top females.

While genomic PTAs are not as accurate as evaluations based on thousands of daughters, the reduction in generation interval and increased confidence in female evaluations have accelerated genetic progress.

Genomic Testing for Complex Traits

Genomic testing is expanding beyond traditional traits like milk yield to include traits that are challenging to measure directly. For example, Bovine Respiratory Disease (BRD) complex is a leading cause of calf mortality, but a lack of extensive disease records has hindered efforts to select for resistance. Genomic PTA for resistance to BRD and other hard-to-record traits, such as feed intake, are under development, making these evaluations available to dairy producers.

Emerging Technologies in Dairy Cattle Genetics

Key technologies in dairy cattle genetics include artificial insemination, embryo transfer, in-vitro fertilization, sexed semen, and now genomics. Looking to the future, several emerging technologies could further impact the field:

1. Transgenic Technologies and Gene Editing: Genetic modifications, such as adding a resistance gene to a cow’s genome to prevent a specific type of udder infection, have the potential to dramatically change animal breeding. These technologies could ensure animals are not susceptible to certain diseases, enhancing productivity and animal welfare. However, they are controversial and raise questions about food safety, international trade, intellectual property rights, and farmers’ ownership of their cows’ reproductive rights.
2. Cloning: While cloning on its own does not accelerate genetic gain—because it prolongs the generation interval—it could be useful when combined with transgenic technologies. For example, if a highly specialized cow is genetically engineered, her genetics could be disseminated to commercial producers through cloning rather than through her son’s semen.

Conclusion

The advancements in dairy cattle genetics over recent decades highlight the importance of slow, steady genetic selection as a tool for achieving long-term progress. While there are always trade-offs, dairy breeders have successfully bred cows that use resources more efficiently without compromising structural integrity or udder health. The future of dairy genetics will likely continue to evolve with the integration of new technologies, creating opportunities for further innovation in animal breeding.