Dairy cattle genetics


Source: University of Minnesota Extension, Joe Armstrong, DVM, and Brad Heins, Extension educators

Quick facts

  • There are several genetic evaluation tools that make interpreting dairy genetics easier.
  • Sire selection is the fastest way to make improvements in herd genetics.
  • Crossbreeding and choosing the best breed of cattle for each farm is important.
  • Farmers should have goals and know what traits are most important for their farm to focus on.

How are dairy genetics measured?

Genetic indexes are effective tools in measuring dairy genetics. Most indexes use a combination of traits to select animals that excel in a certain area that farmers want to focus on.

Consider the reliability of traits when reading a bull proof and selecting animals to mate.

Predicted transmitting ability (PTA)

Predicted transmitting abilities (PTA) is a genetic evaluation tool that allows a comparison of two animals. PTA’s are estimates of an animal’s genetic value for a given trait that will be passed to offspring.

Traits include milk, protein, fat, somatic cell score, calving ease and many more.

For PTA’s, the average for every trait is zero. An animal with a positive number is better than average for that trait and an animal with a negative number is worse than average for that trait.

  • PTA’s are specific for each breed, meaning they cannot be used to directly compare two animals from different breeds.
  • Each PTA trait will have a reliability number expressed as a percentage.
  • The more information that is available the higher the reliability of the reported PTA.

Lifetime Net Merit (NM$)

Net merit is an index of several PTA traits that are of economic importance. A formula is used to combine the traits and give more significance to traits that influence lifetime profitability more than others.

  • The Net Merit index is expressed as a dollar amount.
  • Animals with a higher dollar amount will make more money during a lifetime for a producer on a purely genetic basis.
  • Net Merit is widely used to rank animals for commercial dairy herds.

Breed-specific indexes

Many breeds have indexes that combine PTA’s using specific formulas to provide an overall ranking or score for an animal’s genetic merit. These indexes are similar to Net Merit, but the formulas are often slightly different resulting in different rankings of cows or bulls.

Total Performance Index (TPI)

TPI uses traits from several categories such as production, health, fertility and conformation to provide a ranking of Holsteins based on genetic merit.

Jersey Performance Index (JPI)

JPI provides a ranking of the genetic merit of the Jersey breed using a weighted formula of PTA traits to identify animals to improve lifetime net income.

Does the bull or the cow make a bigger genetic difference?

The fastest genetic progress is made with sire selection. While cow families and pedigrees are incredibly important, sire selection usually makes up more than half of the equation in terms of genetic progress.

Breed choice

One of the biggest genetic decisions a producer can make is what breed or breeds they will have on their farm. While production factors and economic decisions play a huge role in the decision, there are many other factors including tradition, what a producer has now, what breed the kids would like to show, etc.

Breeds will differ on the size of the animal, milk components, production and temperament. The decision for each producer will be based on the market, personal preference, facilities and various other economic factors.


Crossbreeding is breeding an animal from one breed to an animal of a different breed. Often, on a dairy, this is done by using a bull of a different breed on the majority of the cowherd.

  • Crossbreeding started in the United States when farmers began using Jersey sires on Holstein heifers and cows to take advantage of Jersey’s high calving ease.
  • Crossbred animals can have increased fertility, increased longevity and increased health, which all lead to increased profitability.
  • The resulting increases of beneficial traits from crossbreeding is termed heterosis and is sometimes referred to as hybrid vigor.

What farmers should select for

Producers should identify their overall genetic goals or preferences for their farm and select animals based on the specific needs of their dairy.

Use genetic indexes

  • Producers should avoid selecting sires or dams based on single traits.
  • Genetic indexes such as Net Merit, TPI and JPI provide a data-driven method to select animals.
  • Genetic companies usually have animals grouped according to different producer goals.

Production of milk and milk components

  • Producers are paid on the production of milk and milk components (fat and protein). This provides a variety of economic strategies for each individual dairy to choose from.
  • For example, one producer may select for milk production (volume) while another may choose to focus on selecting for milk fat.
  • The two different strategies could both be economically similar and are dependent on individual dairy farm management.

Longevity, fertility and health traits

Productive longevity is the biggest factor for the lifetime profitability of each cow on your operation. Genetic indexes include traits for longevity and health.

  • For a cow to maintain productivity, she needs to become pregnant in a timely manner.
  • Fertility is included in genetic indexes and can be selected for to help achieve high pregnancy rates.

Health traits are also tied closely to productive longevity and profit.

  • Producers can select sires and dams with decreased risk for certain health issues such as milk fever, mastitis, ketosis, retained placenta, metritis and displaced abomasum (DA).