The Growth and Evolution of Health Traits

 By Jaclyn Krymowski for American Dairymen Magazine

 Health traits and their genetic selections are a hot topic and growing interest across the dairy industry. Due to their low heritability, they can be tricky to work with but have a high payoff in economic value because of their potential cost savings. In days gone by, a 1998 study in the Journal of Dairy Science noted a negative relationship between production and health/fitness traits, largely due to the impact of genetic selection exclusively focusing on production rather than wellness at the time. However, the economics around the cost of treatments have changed dramatically since then making the correlation between production and wellness more positive and profitable.

Why breed for health?
Health traits are a powerful tool against disease. Essentially, they’re a literal application of the old idiom “an ounce of prevention is worth a pound of cure.” Animal welfare is an industry issue also fueling the widespread utilization and research of health as a genetic component. From a practical view, the shortage of food animal veterinarians coupled with the growing cost of animal treatment makes prevention a very attractive avenue for producers everywhere. That aside, dairymen using health as one of their advantages must be mindful to keep this breeding as one part of a balanced strategy that still includes things such as fertility, milk production, productive life, and the like.
Even with favorable genetics, the environment is still a major factor in disease prevention. The lower the heritability of any given trait, the higher variability the environment has. The average genetic heritability for traits pertaining to health and wellness tend to be only 5% or less. Of the researched traits recently released to the public sire evaluations, the highest (mastitis) heritability is only 3.1% and the lowest (hypocalcemia) is 0.6%.

Increasing industry application
The Holstein sire evaluations released in April of this year incorporated six different health traits. These were mastitis, metritis, retained placentas, hypocalcemia, displaced abomasums, and ketosis. Other breeds intend to also add this data in their upcoming evaluations when each has enough information collected. The Council for Dairy Cattle Breeding (CDCB) selected these primarily because they were among the most costly and common health issues. They also considered things such as preliminary research, incidence rate, data reporting consistency, cost, and heritability. According to the CDCB’s recent “New Genetic Evaluations for Health Traits - Frequently Asked Questions” fact sheet, “The traits are defined as disease resistance. Health evaluations will be presented as percentage points of event resistance above or below the breed average, with evaluations of cows born in the base year averaging zero. Favorable values for resistance to the health event will receive positive values.” Producer record data was collected through DHI and taken from a variety of affiliates’ herds the U.S.
The interest in exploring the genetic avenues of animal health isn’t just for cows. Other industry companies are looking to pave the way for young stock. Zoetis very recently announced they were adding three new calf wellness traits to their genomics service, Clarifide Plus. These are livability, respiratory disease, and scours. They also have developed their own index designed specifically for calves, the Calf Wellness Index which incorporates all three traits.
Currently, the reliabilities of the CDCB traits are in the 40-49 range for young animals, and in the 44-56 range for progeny-tested animals, with variance among the different traits. As time goes on and more data continues to be collected, the reliabilities will increase. However, the CDCB indicates there are already strong correlations with the new health traits to already existing production and type traits. Some notable ones include productive life, livability, daughter pregnancy rate, and cow conception rate. For example, the strongest known correlation is between somatic cell score and mastitis.
The CDCB cites 2017 research that gives a direct cost estimate for the treatment cost of each trait on a per case basis. That broke down to $34 for hypocalcemia, $197 for displaced abomasums, $28 for ketosis, $75 for mastitis, $112 for metritis, and $68 for retained placentas. These cost estimates do not factor in other costs included in the Net Merit index, “such as declines in production or fertility.”
This new launch hopes to focus on the data analysis and widespread industry education on the impact of each individual trait. The CDCB states that no date has yet been determined on when these new traits will be incorporated into the lifetime Net Merit index.