Interim EPDs
What is an interim?
Interim EPDs are calculated on animals during the time period between the weekly American Angus Association National Cattle Evaluations (NCE). An interim value is indicated by an "I" in front of the number. While admittedly low in accuracy, an interim value gives you a snapshot of the animal's value as a parent, and, thus, it provides a temporary selection-decision tool until the next NCE run in which enough information is available to calculate a true NCE EPD.
How is an NCE EPD different?
The EPDs from the weekly NCE have no letter "I" preceding the EPD. These are calculated using all available performance data for a particular trait, accounting for relationships among animals.
The EPDs resulting from NCE have varying accuracies, depending on the amount of information (the animal's own record, progeny records, ancestral records, etc.) that contributes to each animal's predicted genetic value. To be included in the NCE runs, a nonparent animal must have a performance record or genomic result that meets data requirements.
Parent animals have progeny with performance records and are incorporated into the evaluations even if the parent does not have an individual record for the trait of interest. The evaluations to generate EPDs utilize many generations of pedigrees.
Genomic results are included in the weekly NCE EPDs. Interims do not include genomics.
Interims using the calf's own performance
The best case is when interims have the calf's own record relative to its contemporaries included in the prediction. For example, a bull calf's adjusted 205-day weight relative to his contemporaries plays a role in calculating the interim weaning weight (WW) EPD. The calculations take into account the EPDs on the calf's sire and dam, too.
I-EPD = (0.5 × EPD of sire) + (0.5 × EPD of dam) + (0.5 × Mendelian sampling effect)
The Mendelian sampling effect predicts how the calf's own genetic value deviates from the average of his parents. This is the place where the calf's individual performance relative to his contemporaries plays a role. This interim would typically have an accuracy value of 0.20 to 0.30, depending on the trait.
Interim with pedigree only
In this case, only pedigree information, sometimes called a pedigree index, is involved in calculating the interim EPD. As an example, if a bull calf has no contemporaries and his parents have true NCE EPDs, then a pedigree-estimated EPD is computed as an average of the parental EPDs. The accuracy on the resulting interim is low, at 0.05.
I-EPD = (0.5 × EPD of sire) + (0.5 × EPD of dam)
The most common answer to the question, "Why doesn't this animal have EPDs?", traces to the parents not having true NCE EPDs from the biannual evaluation. In many cases it is the dam that has interims. It is not possible to generate an interim EPD on an animal if one or both parents have interim EPDs without an individual weight record on the calf submitted in a proper contemporary group (at least two calves of the same sex, managed the same and weighed at the same time).
Once weights or genomic results are turned in on the calves, the parents will become part of the NCE run (now having progeny), and the calf in question would have EPDs.
The individual weights on embryo transfer (ET) calves generally are not used in the interim EPD calculation. However, if the ET calves are raised by registered Angus recipient cows, in a contemporary group of ET calves also raised by registered Angus recipients, we are able to incorporate the individual ET calf data into the interim calculations and the NCE.
ET calves out of commercial recipient dams receive only a pedigree-estimated interim EPD with a 0.05 accuracy, since the EPD is just the average of the sire EPD and the donor dam EPD. If the donor dam has interims, the ET calf will have no interim EPD.
Interim EPDs are temporary in a sense. We expect the typical animal to progress toward NCE EPDs, either by way of its own record or progeny data entering into the evaluations. The NCE EPDs take into account much more information than interims. Do not be shocked if the NCE EPD is not the same as the interim EPD.
Sometimes we invest too much confidence in an interim, as if we never expect change. EPDs change. Interim EPDs have low accuracies. Let's not forget that lower-accuracy animals are expected to have changes in their EPDs as more information becomes available on their genetic merit.
A calf with a pedigree-estimated interim EPD has a 0.05 accuracy associated with it. The animal's own performance is not included in the interim calculation. Even on interims that include the calf's own performance, the accuracies are still typically below 0.30. Utilize the possible-change tables available through the Association to help manage the interval of change expected on EPDs at a given accuracy level. Details on possible change associated with accuracy values are located here.
Also, don't be surprised to see bulls with a mixture of interim and NCE EPDs. It is a reflection of how much information was available to compute each EPD at the time the NCE was run.
GUIDELINES FOR WEANING WEIGHT INTERIMS
- The animal must have registered parents.
- The animal must have been weighed at weaning with at least one other animal of the same sex in a proper contemporary group with not more than three days between weigh dates.
- Interim expected progeny differences (EPDs) are not calculated from interims of parents if the animal has no weight record.
- Individual weights of embryo transfer (ET) calves raised by registered Angus recipient cows are used for interim EPDs and are included in the National Cattle Evaluation (NCE).
- Individual weights of embryo transplants raised by nonregistered Angus recipient cows are not used in interim or NCE EPDs.
Note: An animal's own weaning weight must meet all data edits required for NCE, in addition to being from a proper contemporary group.
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