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Expected progeny differences for an category of economically relative traits usher in a new age of genetic selection accuracy.

Selecting genetics for economically relevant traits (ERTs) in the cattle business has typically been akin to driving cattle from Fort Worth to Dodge City, via Seattle.

Rather than aim directly at the desired trait, producers often must settle for emphasizing presumably related traits. Instead of selecting for calving ease itself, as an example, producers have relied on such calving ease indicators as birth weight and pelvic area. Until now.

“I think these are some of the most valuable tools available to us as animal breeders. They give us information about economically relevant traits, selection tools that we've never had before,” says Donnell Brown of the R.A. Brown Ranch, Throckmorton, TX.

Specifically, Brown is describing the opportunity he sees in the industry's first Reproduction Sire Summary released by the Red Angus Association of America (RAAA) in May. Besides the industry-standard fare of expected progeny differences (EPDs), mostly indicator traits, the new summary provides a suite of EPDs for reproductive ERTs, including heifer pregnancy, stayability, direct calving ease and total maternal calving ease.

“Our goal is to comprehensively describe Red Angus for reproduction, growth and carcass traits, using as few different EPDs as possible. Since reproduction is the most economically important area of traits in cow/calf production, that has been our first priority,” explains Bob Hough, RAAA executive secretary.

In a nutshell, rather than predict trait differences between sires in units of size and weight like most EPDs, reproductive ERTs predict the difference in probability of success or failure for each trait (Figure 1):

  • Calving ease direct — the probability a sire's calves will be born unassisted.

  • Heifer pregnancy — the probability a bull's daughters will conceive to calve as a 2-year-old.

  • Calving ease total maternal — the probability a bull's daughters will be able to calve unassisted.

  • Stayability — the probability that a bull's daughters will remain in the herd beyond the point of breaking even, defined as 6 years of age.

In fact, the either/or nature of these categorical traits is one reason complete development took so long.

“This summary is the culmination of 10 years of effort between Red Angus breeders and researchers at Colorado State University,” says Hough. It took researchers that long to develop threshold models for calculation, which could account for the non-linear qualities of these traits.

Red Angus was the first breed to introduce a stayability EPD seven years ago. They debuted heifer pregnancy exclusively last year and then introduced the two snapshots of calving ease this year.

Besides pinpointing the aim of selection, ERTs also address the frustration of producers who try to incorporate more and more EPDs into selection decisions. Because ERTs incorporate other EPDs into their calculation, more information can be transformed into fewer, more meaningful selection considerations.

“If you can measure it, you can create an EPD for it,” says Hough. “Instead of seeing how many EPDs we could create, we decided to see how few we could use to describe the most economically important areas.”

For example, both calving ease EPDs incorporate birth weight data. Over time, that may mean that while a birth weight EPD is still calculated as a useful component of calving ease, it may no longer be published some day because it's been combined with calving ease scores into a single, more useful prediction.

While Brown isn't ready to disregard birth weight EPDs, he does say, “If it's a bull with a high accuracy that has been used on heifers, I'll put a lot more weight on the calving ease EPD than the birth weight EPD.” He has plenty of experience using the calving ease EPD developed for Simmental cattle more than 20 years ago.

Likewise, the heifer pregnancy EPD can incorporate scrotal circumference data. Hough, however, says RAAA has concluded scrotal circumference isn't indicative of anything useful in their breed, so they no longer publish it.

Lowell Gould, RAAA genetics and information systems director, emphasizes, “The RAAA philosophy on EPD development is that an EPD should only be developed if the trait it represents is directly related to a revenue or an expense. This philosophy allows Red Angus to be described with the fewest number but most meaningful EPDs possible.”

Consequently, some indicator traits producers traditionally apply to their selection decisions may shift in importance over time as they are folded into ERTs.

Catching A Slow Wave

So far, this possibility exists only in the Red Angus breed and a couple of others with ERTs for one or two traits. A key reason Red Angus has been able to develop reproductive EPDs for ERTs is why some breeds may find such calculation difficult.

Total Herd Reporting (THR), which RAAA adopted seven years ago, requires all Red Angus cows be reported, even if her calf is not. Only one other widely used breed requires this; the rest use Voluntary Herd Reporting in which registering calves isn't contingent on reporting cow data.

Subsequently, while it's possible to calculate ERTs with data submitted on an optional basis, presumably on fewer cows, Hough believes, “THR makes this possible and unbiased. It's fundamental to providing this kind of information accurately.”

Besides, Hough says, THR allows assumptions on the biological distribution of the data. This means abnormal data can be filtered out. For the record, several breeds recently have attempted to adopt a THR model of performance reporting but have been lambasted by their breeders as being too regulatory.

Arguably, part of the reluctance might have to do with perceptions about how current genetics will rank in measures that get at traits directly. Or downright confusion. For example, while it may seem intuitively impossible for a bull siring females with superior stayability — sustained fertility over time — to be inferior for heifer pregnancy, Gould says the two types of fertility are actually different traits. That underscores the value of EPDs, which measure ERTs versus indicator traits.

“It opens up a whole new train of thought on these cattle because the reality is that the facts don't lie,” says Brown. It also makes sorting easier by thinning the list of potentials.

“I'm selecting for bulls that don't make mistakes, bulls at least better than breed average for every trait,” explains Brown. “The more tools we use in selection, the shorter and better our list of sire options becomes. Most importantly, the commercial cow man wins because he can more easily and accurately select bulls to fit his needs.”

To be included in the inaugural RAAA Reproductive Sire Summary, bulls must: have been progeny recorded during the last two years, have a minimum accuracy for weaning weight EPD of 0.5 in the spring 2002 sire evaluation, and have genetic predictions for all of the reproductive EPDs. All told, 1,482 sires met the first two criteria; only 527 met all three (Figure 2).

“Where the industry used to take homerun hitters — bulls that excelled in one or two traits — and mass multiply those, we discovered they also struck out a lot of the time in other traits. Now we're mass multiplying the cattle with a better earned run average, Brown says.

Figure 1. Interpreting EPDs for reproductive ERTs

Rather than predict trait differences between sires in units of size and weight like most EPDs, reproductive EPDs predict the difference in probability of success or failure for each trait. For instance, consider this example of heifer pregnancy — the probability a bull's daughters will conceive to calve as a 2-year-old:

Sire Heifer pregnancy EPD*
A +1
B +14
Difference +13%
In this example, Sire B is predicted to sire daughters 13% more likely than those by Sire A to produce daughters that will conceive to calve as 2-year-olds.
*Accuracy assumed to be the same

Figure 2. Averages for Red Angus reproductive traits*

Trait Minimum Average Maximum
CED -12 4 23
HPG -9 7 21
CETM -9 4 20
ST -6 9 20
*CED = calving ease direct; HPG = heifer pregnancy; CETM = calving ease maternal; ST = stayability.
Source: Red Angus Association of America