Holstein breeders making sire selection and breeding strategy decisions will have genetic information directly related to herd health beginning in April 2018.

Natzke dave
Editor / Progressive Dairy

Addressing participants at the Council for Dairy Cattle Breeding (CDCB) annual meeting, held Oct. 3 in conjunction with World Dairy Expo, CDCB geneticist Kristen Gaddis outlined the six new health traits to be included in official sire evaluations. The traits will identify resistance to:

  • Hypocalcemia (milk fever): Typically results after calving due to low total blood calcium levels

  • Displaced abomasum: Enlargement of the abomasum with fluid or gas causes movement to the left or right of the abdominal cavity and usually requires veterinary intervention

  • Ketosis: Build-up of ketone bodies that typically occurs due to negative energy balance in early lactation

  • Mastitis: Infectious disease that causes inflammation of the mammary gland; one of the most common and costly diseases of dairy cattle

  • Metritis: Infection of the endometrium, or lining of uterus, after calving

  • Retained placenta: Retention of fetal membranes more than 24 hours after calving

Gaddis said these diseases were selected for their significant incidence rates and costs to dairy farmers, the ability to consistently identify and record health events related to these diseases, and trait heritability.

Reading the evaluations

When reading the evaluations, the health traits will be presented as a percent of disease resistance of an individual animal compared to the breed average. A positive value indicates greater resistance than breed average while a negative number indicates resistance lower than breed average.

For example, the Holstein breed average incidence of mastitis is 10 percent. If a sire’s mastitis resistance evaluation is +3, it means his daughters, on average, will have a mastitis incidence of 7 percent, with a resistance rate of 93 percent. In contrast, if a sire’s mastitis resistance is -4, his daughters, on average, will have a mastitis incidence of 14 percent, or a resistance rate of 86 percent.


Trait reliability, heritability

Health trait reliability values are substantially higher for genomically tested animals, ranging from 40 to 49.4 in young animals and 44.2 to 56.3 in progeny-tested animals, and are expected to increase as more information becomes available.

Heritability of these traits is low:

  • Hypocalcemia: 0.6 percent
  • Displaced abomasum: 1.1 percent
  • Ketosis: 1.2 percent
  • Mastitis: 3.1 percent
  • Metritis: 1.4 percent
  • Retained placenta: 1 percent

However, since genetic resistance is accumulative and permanent, disease resistance can be built up over time (How selection for better health impacts dairy profitability).

Trait correlation

According to Gaddis, many of the new health traits have significant correlations with Productive Life, Livability, Daughter Pregnancy Rate and Cow Conception Rate. The strongest correlation is between somatic cell score and mastitis resistance.

Displaced abomasum resistance has the largest correlation with Livability, meaning animals with displaced abomasum are much less likely to survive in the herd. There are no significant correlations with protein yield.

Individual traits, indexes

PTAs will be published for the six individual health traits beginning in April. (Editor's note: Originally, the new health traits were scheduled to be incorporated into the Net Merit$ index in April. That decision was recently reversed and there are no changes planned for the Net Merit indices in April. The timing of when health traits would be included in Net Merit indices is not yet determined.)

What’s ahead?

While initially available just for Holsteins, health traits for other breeds will be added as more information for each breed is accumulated.

The industry will get a sneak peek when the new health traits are released as “preliminary evaluations of individual animals” in December, distributed through Dairy Records Processing Centers, A.I. organizations, breed associations and nominators. Based on partial data, the results will not be published but may be used for educational purposes.

CDCB is developing educational materials about the new evaluations. These will be distributed to all industry stakeholders and dairy producers through popular press articles, informational e-mails and fact sheets.

For more information, download “New Genetic Evaluations for Health Traits: Frequently Asked Questions”  end mark

Based in Bowie, Maryland, CDCB is a collaborative effort between four sectors of the U.S. dairy industry: dairy records providers, dairy records processing centers, National Association of Animal Breeders and Purebred Dairy Cattle Association.

Dave Natzke