Selection indexes help cow-calf producers determine what traits are best for their herds.
Flip through the pages of a bull sale catalog or pull up pedigree information on a specific registered animal and the amount of information is almost overwhelming. Processing the long list of production, maternal and carcass EPDs may leave producers scratching their heads, trying to determine which traits to place more emphasis on to fit the diverse needs of the beef business.
“Most breeds publish a whole range of EPDs for a variety of different traits. We expect our seedstock and commercial producers to make sense out of all that data,” says Bob Weaber, cow-calf specialist with Kansas State University Extension. “In a multiple-trait selection process that becomes very difficult, if not impossible.”
Different traits provide different economic benefits, depending on a herd’s marketing strategy and production scenario. For example, if a producer sells calves at weaning and keeps replacement heifers, placing all the selection pressure in sire selection on carcass traits creates a disconnect between selection and marketing. The producer in this scenario doesn’t have much opportunity to capture the carcass value of the calves and eliminates selection pressure on calving ease, weaning growth and maternal traits that are the most economically important. Applying equal pressure to all the traits with EPDs dramatically limits progress in those that are the most economically important. Single-trait selection, while providing the most opportunity to change a single trait, leaves out other traits of importance and generates significant genetic risk.
Simply put, applying selection pressure across EPDs is a fine dance, so how do producers know when to give and when to take?
Selection indexes — genetic trade-offs
Throw it back 71 years. Dr. Lanoy N. Hazel, a young student with a bright future was working on his graduate degree at Iowa State University when he came up with the concept of selection indexes, also known as selection indices. This concept involved creating a system to appropriately weight multiple traits so selection could be made with fair analysis of the value of a one-unit gain in a trait, while all others held constant. Therefore, economic weightings are only put on traits economically important to the producer’s end point.
“As EPDs were developed, most research focused on improving the methods used to document the genetic merit of individuals, and many of the researchers recognized that was only part of the solution,” Weaber says. “The other was appropriately weighting the genetic predictions (EPDs) by their contribution to profit and aggregating those into a single value to use in selection to some specific end point.”
In the 1943 journal of Genetics, Hazel explained the complicated process quite simply:
The idea of a yardstick or selection index for measuring the net merit of breeding animals is probably almost as old as the art of animal breeding itself. In practice several or many traits influence an animal’s practical value, although they do so in varying degrees. The information regarding different traits may vary widely, some coming from an animal’s relatives and some from the animal’s own performance for traits which are expressed once or repeatedly during its lifetime...These factors make wise selection a complicated and uncertain procedure; in addition fluctuating, vague, and sometimes erroneous ideals often cause the improvement resulting from selection to be much less than could be achieved if these obstacles were overcome.
According to Weaber, the swine and poultry industries were the first to embrace this technology, as early as the 1950s, since production practices were closely related across the country and breeding decisions were controlled by fewer decision makers. It wasn’t until the mid-2000s when the beef industry was able to follow suit with several breeds releasing generalized indexes designed to fit most production and marketing scenarios.
“For a long time they were only making selection with half the set of tools they needed to have available,” he explains. “The implementation of selection indexes in beef cattle has helped bridge the gap of multiple-trait selection and using our current EPDs in genetic evaluation.”
Putting them to use
The first step for producers to set a direction for genetic improvement in their cow herd is to have a specific breeding objective and program direction. This will help keep producers from straying too far away from the traits most pertinent to reaching their endpoint. Their written description of their breeding objective should include things like forage and labor availability, marketing endpoint and replacement strategy. Next, producers need to focus on the selection index that best fits their program’s goals.
“One of the key things for producers to remember when using selection indexes is making sure the one chosen is aligned with their marketing endpoint,” Weaber stresses. “Sometimes I’ll see a terminal selection index (carcass traits) used in making a bull purchase decision and then calves are sold at weaning time — so there can be a huge disconnect. If producers do that, then they aren’t making near as much progress on traits that are the most economically important to their program.”
But on the flip side, producers seeking a terminal sire bull for use in a system that retains ownership and sells calves on the grid should avoid indexes focused on pre-weaning traits.
One question that is regularly addressed to Weaber is how to use a selection index to make a mating decision when AI-breeding first-calf heifers. He suggests producers utilize the sire summary search tools on breed associations’ websites where selection criteria can be customized. For example, a producer doesn’t want to use an Angus bull with a calving ease (CE) EPD less than 8 to help minimize dystocia but also wants to maximize the value of calves sold at weaning. An effective strategy is to sort the bulls by the weaning index ($W) and place a minimum accuracy value of 0.65. Once ranked by index value, producers should consider selection of the first bull that satisfies their CE needs, Weaber says.
Consider a situation where a producer is on the fence about picking out two bulls to fit his CE EPD threshold of 8. Oone has a score of 7.8 and the other a 9; however, the slightly lower CE bull has a $20 advantage on the selection index.
“If you apply the independent culling level first, you’ve eliminated the possibility of his selection. If you sort by index first, then you get the whole list of bulls and can make the judgment,” he explains. “Applying a hardline, independent culling level can cause the omission of bulls that have tremendous index value but just miss the culling level for the auxiliary selection criteria.
“Outside of specific scenarios such as breeding heifers, it’s typically not advised that any other EPDs are put inside the selection decision besides the index, because then traits start to get double counted,” Weaber says.
At the end of the day, making selection decisions is one big balancing act when chasing optimum profit for economically relevant traits for producers.
“Once a producer sits down and writes out the breeding objective and only utilizes selection indexes that are aligned with that plan, they will not only start to see genetic progress in their herd but economic progress as well,” Weaber concludes.