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.
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.
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)
I-EPD = (0.5 * EPD of sire) + (0.5 * EPD of dam)