Proper contemporary group design and reporting is vital to evaluating the genetic potential of sires. You might think reporting all your calves as one contemporary group will make their EPDs more accurate but the reality is you want to assign contemporary groups that reflect how the calves were raised for the best results. Read the following article, originally published in the Register, for further explanation of the main concepts of contemporary grouping.
Contemporary Grouping—a Cornerstone of Genetic Evaluation
By Wade Shafer, Ph.D., EVP of the American Simmental Association, originally published in the Register
This is definitely going to be what my buddies at the Register call a “tech-blue” article. In other words, only read this if you’re serious about breeding cattle—no one is going to be entertained here. But before you turn the page, though discussing contemporary grouping may be as boring as watching paint dry, it’s one of the most critical issues in ensuring an accurate genetic evaluation of your cattle. And, in my opinion, it’s the area that breeders make the most mistakes when submitting their data.
Before wading into a discussion about contemporary grouping let’s start with the definition of a contemporary group. In the context of genetic evaluation, a contemporary group consists of animals that have been exposed to the same outward environment (management system, pasture, feeding group, etc.). I prefaced environment with outward because there is no way to expose animals to an identical environment—we can only sort animals into groups that, from all outward appearances, are treated uniformly.
By grouping animals properly, EPDs can account for differences between animals due to disparity in things like pastures, weather, feed supplementation, and even scales and ultrasound machines—all things we assume animals within a contemporary group are exposed to evenly. If we group animals improperly, EPDs can’t do a good job of accounting for these differences, with the end result being EPDs that aren’t as valid and informative as possible.
Improper contemporary grouping has the largest impact on low-accuracy animals, i.e., essentially all bulls and females sold each year. For example, if a group of bull calves were fed extra for show and lumped into the same group as their herd mates, growth EPDs will be: 1) inflated for the show calves, their dams and possibly their sires (if lower accuracy), 2) deflated for their herd mates, their dams and possibly their sires (if lower accuracy).
I could expand the cascade of effects beyond the calves and their parents (e.g., sibs, cousins, etc.), but you get the picture—grouping cattle improperly can cause problems. Fortunately, the problems subside and eventually become nonexistent as more data comes in on an animal, unless there is a systematic reason for an animal’s offspring to be improperly grouped. (e.g., if breeders are inclined to improperly group show calves, a bull tending to sire them may be a candidate for inflated growth EPDs.)
The previous example is an obvious one. We all know that animals given favorable treatment shouldn’t be grouped with animals that haven’t. However, there are many not-so-obvious situations. An area where missteps often occur is in identifying animals that shouldn’t have any contemporaries. Though an animal designated as a twin, embryo transplant, orphan or foster calf are automatically removed, there are many other reasons to remove an animal from a contemporary group. The rule of thumb is that any animal exposed to an identifiably different environment from the rest of its contemporaries should be singled out, e.g., calves nursing multiple cows, chronically ill, or injured or calves having ill or injured dams. By sorting these animals from their contemporaries their performance information does not enter the genetic evaluation and therefore does not unfairly impact their own or other animals’ EPDs.
Though many animals are left in contemporary groups that shouldn’t be, in my estimation, the most common problem is the grouping of calves reared in different pastures. If you get nothing else from this missive, I want to make it absolutely clear that calves raised in different pastures should be in separate contemporary groups at weaning.
There seems to be the perception that breeders’ calves can be grouped together even if they were reared in different pastures. This may be due to the misconception that differences between pastures on the same ranch are minimal. The truth is that the disparity between pastures is often much greater than what breeders think. Studies have shown that, even when adjacent, pastures with no visible difference can cause significant differences in performance. If not grouped properly (separately), these differences can lead to the same undesirable effect on EPDs as described above.
Another rationale behind mass grouping may be due to the perception that larger contemporary groups yield more accurate EPDs. My straightforward response to this is that your EPDs will be more valid and informative if you follow the book and group calves by the pastures in which they were reared. My roundabout response is that the relationship between accuracy and contemporary group size isn’t as straightforward as people think.
I’ll use the following example to illustrate: Let’s say we have weaning weights on 15 calves apiece by three sires. Let’s also say they were raised in three different pastures with five calves from each sire per pasture. If we ignore the rules and group all 45 calves together, it is true that the calves’ EPDs will have a slightly higher calculated accuracy than if we went by the book and sorted them into 3 contemporary groups. On the other hand, grouping all the calves together will actually lower their sires calculated accuracy compared to placing the calves in 3 groups. The impact on sire accuracy may be surprising at first glance, but it does make intuitive sense; we would certainly put more faith in a sire tested across multiple management scenarios and physical environments than a single-contemporary-group proof.
You may have noticed that I prefaced accuracy in the previous paragraph with calculated. Calculated accuracy refers to the accuracy ASA’s genetic evaluation system will calculate based on the information you submit. My intent was to differentiate between calculated accuracy and what you, as a conscientious breeder, are actually after.
As the above example shows, large contemporary groups tend to raise the calculated accuracy on calves while spreading those calves among multiple groups raises the calculated accuracy on their sires. But calculated accuracy shouldn’t be what you’re concerned with—you want EPDs as close to your animals’ true genetic value as possible. Grouping your calves by the pasture they were reared in will go a long way toward ensuring that. Whether that means all your calves are in one group or they are sorted into several, at least you and your customers will have the piece of mind in knowing that your EPDs are as accurate (i.e. valid and informative) as you can make them.
To familiarize you with the tools required for contemporary grouping, I’ll close with the codes that determine how contemporary groups are formed at the ASA:
Sex code: 4 = B = bull; 6 = F = female; 5 = S = steer. All animals are sorted into contemporary groups by sex designation.
Multiple Birth code: 1 = S = single; 2 = TS = twin, same sex; 3 = TR = triplets; 4 = TO = twin, opposite sex; 6 = FE = frozen embryo; 7 = ET = embryo twin, same sex; 8 = ET = embryo twin, opposite sex; 9 = ET = embryo transplant, fresh. Data are not included in genetic evaluation on anything coded over 1 until it becomes a parent.
Calving Unit code: used to designate dams that have been exposed to unequal environmental conditions during gestation not covered under the multiple birth code, e.g., cows in different locations or fed different rations. The designation must be a single alphanumeric character (i.e. A-Z or 0-9).
Weaning Management code: 1 = D = dam only; 2 = C = dam with creep; 3 = B = without dam, bucket fed; 4 = T = twin or foster dam. Data are not included in genetic evaluation on anything coded over 2 until it becomes a parent.
Weaning Pasture Unit code: used to designate calves that have been exposed to unequal environmental conditions between birth and weaning not covered under the weaning management code. For example, calves that were in different pastures, treated specially, injured, or chronically sick. The designation must be a single alphanumeric character (i.e. A-Z or 0-9).
Yearling Feeding Unit code: used to designate calves that have been exposed to unequal environmental conditions between weaning and yearling. For example, calves that were in different feeding groups, injured or chronically sick. The designation must be a single alphanumeric character (i.e. A-Z or 0-9).