Understanding and Using Maternal EPDs - October 2021

Understanding and Using Maternal EPDs by Ryan Boldt, Director of Breed Improvement

RAAA publishes several EPDs created to improve the genetic merit of retained females. There are several categories that these EPDs fall into such as fertility, longevity, easy calving, mature size and calf growth. Each of these EPDs is designed to help improve the genetic merit of females for these traits. However, it’s good to review what each EPD is predicting, as well as if a lower or higher value is more favorable for each trait.

The Stayability EPD predicts differences in retained daughters’ ability to remain in the herd and produce a calf through six years of age. Six years has traditionally been the breakeven point for a cow to offset her development costs as well as the costs of other females that have fallen out of the herd. Previous work has shown that within the RAAA database, females out of sires with higher Stayability EPDs had, on average, one more calf over their lifetime than sires with low EPDs. These EPDs are expressed on a percentage basis, and therefore, a higher value is more favorable for STAY.

A second EPD important for making better replacement females is Heifer Pregnancy (HPG). This EPD predicts differences in the percentage of daughters that will become pregnant during their first breeding season and calve as 2-year-olds. Heifer Pregnancy EPD is a direct look at fertility during a female’s first breeding season. Research has shown that females that conceive early during their first breeding season tend to do so over their lifetime, which results in more productive females. This EPD is expressed as a percentage and a higher value is more favorable.

The largest expense in a cow-calf operation is the cost to feed the cowherd. Of this expense, 65% to 70% of the energy input issued to maintain weight and body condition score. The goal of the Maintenance Energy EPD is to provide a tool that allows for selection to lower maintenance energy requirements. This EPD incorporates information from mature weight as well as milking ability of the animal for the EPD calculation. The ME EPD is expressed as Mcal per month. This then predicts the difference in those requirements to maintain adequate weight and condition. For this EPD, a lower value is more favorable because less energy is required to maintain the animal.

The final EPD that can be included in the list of important female-building traits is the Milk EPD. This EPD predicts differences in weaning weight of calves from an animal’s daughters. The important factor here is that it is expressed in pounds of weaned calf weight. It’s also important to consider environmental constraints when evaluating the Milk EPD. Previous research has shown that matching milking ability to the environment is helpful for commercial producers. This EPD is expressed in pounds and a higher value is generally more favorable.

While each of these EPDs are important individually, it often becomes difficult to weigh out what is the most profitable combination of these traits.

The goal of the HerdBuilder index is to economically measure maternal traits that affect profitability from conception to weaning. The traits included in the HerdBuilder index include measures of fertility, mature size, calf weights, calving ease and longevity. This index simplifies the tradeoffs and advantages of each of the traits and boils it down to a single number. Since this index is expressed as dollars per head, a higher value is more favorable.

RAAA offers one of the most comprehensive set of EPDs that relate to building better replacement females. These tools have helped shape the Red Angus female as the most-favored in the industry!