Genomic Testing and Net Merit: Choosing Holstein Heifers and Sires by the Numbers

A generation ago, choosing the sire for a heifer meant reading a proof built from the records of his daughters, which took years to arrive. Today a calf can be tested for DNA soon after birth, and her predicted genetic merit is available long before she calves. Genomic testing is now one of the biggest tools in dairy breeding, and understanding it is useful whether you run a commercial herd or breed show cattle.

This guide explains what the numbers mean and how farms use them. Evaluation methods and indexes are updated regularly by the organizations that run them, so check current documentation before making expensive decisions. If you want to find dairy genetics events near you, agriculture.directory can help you find agriculture events in your area.

Who Produces the Numbers

In the United States, national genetic evaluations for dairy cattle are calculated by the Council on Dairy Cattle Breeding, or CDCB. According to its materials, official genomic evaluations for Holsteins, Jerseys and Brown Swiss began in 2009. Breed associations, such as Holstein Association USA, add their own type and conformation evaluations. CDCB publishes official evaluations on a schedule of three releases a year, with genomic evaluations for newly submitted genotypes calculated weekly, according to a CDCB-authored review in the journal Frontiers in Genetics. See the CDCB page on the effect of genomics and the Frontiers review of the U.S. genomic evaluation system.

What a Genomic Test Does

A tissue, hair or blood sample is sent to a laboratory that reads thousands of small DNA markers. Those markers are compared against a very large database of animals with known performance, producing a prediction of the animal's genetic merit for many traits. A Washington State University Extension publication on genomic selection explains that heifers can be ranked by their genomic merit, such as for net merit dollars, to decide which to keep for breeding and which to cull or sell. The prediction is more reliable than pedigree alone, because it captures which genes the calf actually inherited from her parents rather than the average of what they could pass on.

What the Test Adds

• Earlier, more reliable predictions. CDCB states that genomic evaluations are considerably more reliable than parent average.
• Parentage verification. CDCB can verify, correct or complete the pedigree of every genotyped animal, which improves accuracy and helps control inbreeding.
• Genetic conditions. Tests identify carriers of known genetic defects, so matings can avoid them.
• Inbreeding information. Genomic data show how related an animal is to the population.
• Management uses. CDCB notes that genomic testing has become a tool for mating, culling and selection decisions.

What Net Merit Means

Net Merit dollars, written NM$, is the national economic index for U.S. dairy cattle. A breed association page describes it as designed to maximize a cow's lifetime profitability, ranking animals by their combined genetic merit for economically important traits with weights based on an economic model of income and expense across a cow's life. The value is expressed as predicted dollars of extra lifetime profit compared with a base. CDCB has updated the index periodically, and its 2021 revision added feed saved, heifer livability and early first calving to the traits included. A higher number means higher predicted profit, but the number is a prediction, not a promise, and it depends on the cow's environment and management.

Why It Changed the Industry

The CDCB-authored Frontiers review reports that genomic selection roughly doubled the rate of genetic gain in Holstein bulls, with the average annual increase in net merit of marketed Holstein bulls rising from about 40 dollars a year before genomics to about 85 dollars a year after. CDCB also reports that in 2021 about 71 percent of artificial insemination breedings in U.S. dairy herds were to sires with no milking progeny, which shows how much of the industry now relies on genomic predictions. That speed is a big reason modern Holsteins have improved so quickly in production, health and fertility traits.

Using the Numbers on Your Farm

1. Decide what you are selecting for. Net Merit is a balanced index, but you may emphasize components, fertility, health or feed efficiency, depending on your milk market and management.
2. Test replacement heifers. Ranking them lets you invest feed and housing in the better ones and consider selling or using beef semen on the rest. Our guide to sexed semen and beef-on-dairy explains how that choice fits into a breeding system.
3. Use the data for matings. Pair animals to avoid carrier matings and keep inbreeding low.
4. Check the reliability. A higher reliability means the prediction is more likely to hold. Compare reliability along with the value.
5. Combine with herd records. Your own milk and health records, as in the guide to DHI records, show how animals perform on your farm.
6. Weigh the cost. Testing costs money, so decide how many animals to test and what you will do with the results. The enterprise budget guide shows how to count the cost.

New Traits Keep Coming

Evaluation systems expand over time. Trade press coverage of CDCB's August 2026 release described new fertility refinements and the first genomic predictions for calf health, including resistance to diarrhea and respiratory problems. See the Dairy Herd article on the August 2026 evaluations for details, and check CDCB for official documentation. Health traits matter because they affect cost as much as milk yield does. Our guide to calf scours and pneumonia explains why.

For Show Cattle Breeders

Genomic numbers rank production, health and fertility. A show ring ranks conformation, style and presentation. The two are related but not the same, and a cow with high production merit can be a poor show animal and the reverse. Breeders use genomic data alongside type evaluations from Holstein Association USA, covered in the guide to linear appraisal. Do not assume a high number means a champion, or that a champion makes a profitable cow.

Limits and Cautions

• Predictions are not guarantees. Individual animals vary.
• Narrow selection narrows diversity. Chasing the top few sires increases relatedness across the breed.
• Environment matters. A cow with high merit still needs feed, comfort and care.
• Indexes change. Rankings shift when evaluations are updated.

Common Mistakes

• Testing everyone with no plan. Decide how you will use the results.
• Using only one number. Look at the traits behind it.
• Ignoring conformation and health. Numbers are not the whole cow.
• Overusing a few popular sires. Spread the risk.
• Forgetting carriers. Check haplotype and defect status before mating.

Farm.fm's page on artificial selection explains how breeders shape animals, and for a laugh, see farm.fm's piece on cows that produce 2.6 percent more milk and get punished for working too hard.