Genomic selection is the use of DNA information to supplement the available pedigree breeding information on cattle. It provides breeders with more accurate information to make breeding decisions.

DNA remains the same throughout life and is the same in all cells of the body (for example blood, semen, hair follicles). The reliability of a bull’s ICBF-based proof summarises the likelihood of future fluctuations in the genetic evaluation as more records become available on the individual animal and its progeny or relatives. The index values (star rating) of high-reliability bulls can fluctuate widely over time; this is because the genetic merit of the bull is accurately known based on progeny performance.

Every calf inherits 50% of its DNA from its sire, but this genetic base is a random sample. Therefore, genetic evaluations based on a bull’s progeny performance is simply quantifying whether the sire had good or bad DNA for specific traits. Genomic selection attempts to evaluate the DNA of the individual animal directly, rather than relying solely on the performance of its progeny.

Because DNA is the same throughout life, genetic merit based on DNA can be assessed early. The DNA information can also be used to validate parentage and, where missing or incorrect, assign parentage. This has important implications, not only for more accurate genetic evaluations, but also for the avoidance of inbreeding in future generations.

Accurate

DNA information can also be used to more accurately quantify relationships among animals. For example, pedigree analysis assumes that an animal shares 25% of its DNA with each of its grandparents and thus a grandsire-granddaughter mating would result in an inbreeding level of 12.5%.

In reality, however, this can vary from 0% (none of the DNA transmitted from the grandsire to its progeny was transmitted to its granddaughter) to 25% (all of the DNA transmitted from the grandsire to its progeny was transmitted to its granddaughter); DNA can more accurately quantify the true relationship.

For DNA profiling to work in Ireland, huge databases of animals with DNA information and performance information are required to establish this link. This is the justification of the Beef Genomics Scheme, under which a biological sample from a selection of natural mating bulls and cows was requested. The cows were selected to represent a range of different bloodlines and show the best and worst performing cows. Genomic selection, based on DNA information, was made available to Irish dairy farmers in 2009. In 2014, 60% of semen used in Irish dairy herds was from genomically evaluated bulls; these bulls have no daughters milking. The reliability of the EBI (the dairy breeding index) has almost doubled from 32% to 58%. Many dairy farmers are now routinely genomically testing their heifers to identify those for retention and culling, which is something suckler herd owners can do also. Analysis comparing the DNA-based estimate of the index value of a bull and its daughter-based evaluation has shown that the DNA information into the genetic evaluations improved the accuracy by up to 54%.

Incorporating DNA information into beef genetic evaluations, however, does not alter the fundamentals of beef breeding. Genomic selection continues to exploit pedigree information. Genetic gain is still based on breeding the best with the best to produce the best. The difference is that genomic selection makes it easier to identify the best (and worst) animals. In the future, it is likely that all stock bulls, especially those sold at pedigree sales, will be genomically tested. The cost of genomically testing an animal is about €30; this is very small given the benefit of having a more accurate genetic evaluation.

Most countries are actively working on incorporating DNA information into national beef genetic evaluations with some countries having already implemented it for some breeds. Ireland is to the fore in the incorporation of DNA information into national genetic evaluations in dairy and beef cattle.