One of the American Angus Association's research initiatives is to characterize reproductive traits in the Angus breed. It's perhaps the most difficult class of traits in terms of creating genetic values. Yet, in a beef production system, the economic importance of reproductive success is vital. Seedstock and commercial producers continually ask about the availability of reproductive selection tools to improve their herds. A large database for research enhances the ability to develop genetic predictions, such as EPDs and indexes, for the reproductive complex.

Angus producers are submitting breeding records as part of their performance data. In September 2007, the Association's Board of Directors approved an updated release of heifer pregnancy EPDs on sires with a minimum .30 accuracy in a special research report. The following report summarizes the initial research and resulting EPDs that were developed.

Genetic Evaluation Procedures and Edits

A heifer's breeding record was coded as a success or failure of being pregnant, based on any pregnancy check data or calving information recorded and submitted by the breeder. Heifers were excluded from the analysis if their age at the time of the evaluation did not allow them time to have recorded a calf.

Edited data on heifers were analyzed in a threshold analysis with a full animal model and three generation pedigree. Variance components from research in collaboration with Mark Enns at Colorado State University were used in the analysis representing a heritability of .13.

Contemporary group was defined as breeding herd, breeding year, season, and synchronization code. Data edits included the removal of any contemporary groups with no variation (0% pregnant or 100% pregnant). The final analysis represented 506 contemporary groups from 248 herds.

EPDs were generated on 50,374 animals, as described in Table 1. EPDs are reported on an arbitrary base to illustrate the range and distribution of genetic values.

Figure 1 illustrates the distribution of EPDs for the current sires having heifer pregnancy EPDs generated in the analysis. The EPDs ranged from -3 to +17 on 1,419 current sires, and accuracies were from .05 to .89.

Figure 2 depicts an example percentile breakdown for the heifer pregnancy EPDs for the current sires in the research project. As with all percentile rankings, these values are to be used as a guide to determine where an individual of interest falls within a particular class of animals, in this case the 1,419 current sires with EPDs.

Genetic Trend and Correlations

In evaluating genetic trend for heifer pregnancy, the average heifer pregnancy EPD by animal birth year has remained unchanged over time. The genetic trend line is flat and no trend has occurred for heifer pregnancy based on this initial analysis as would be expected in situations where little selection pressure was applied to heifer pregnancy rates. The review of correlations among other traits using sires with an accuracy of .50 or greater showed that heifer pregnancy EPDs were uncorrelated with scrotal, calving ease, milk, fat (ultrasound and carcass), percent IMF, marbling EPDs, or any growth traits.

Heifer pregnancy EPDs are to be used as a tool to increase the chance of a sire's daughters becoming pregnant during a normal breeding season. The unit of measure for the EPD is a percentage. A higher EPD is the more favorable direction for selection pressure. As with other EPDs, the relative difference among sires is of importance rather than the absolute value.

Figure 3 provides an example of the use of heifer pregnancy EPDs. Assume there are 100 daughters for each of the two bulls, managed and treated alike in the same breeding environment. When comparing the two bulls, one would expect an average of 5 more pregnant daughters out of 100 from Bull A compared with Bull B. Essentially Bull A's daughters have a 5% greater chance of becoming pregnant than Bull B's daughters.

The Fall 2008 research update of heifer pregnancy EPDs on sires has been computed using the American Angus Association's breeding record database. These EPDs are designed to characterize differences among sires in the Angus breed for daughter's heifer pregnancy. When comparing two sires based on their heifer pregnancy EPDs (reported in units of percentage), a higher EPD sire would be expected to have daughters with a greater probability or chance of becoming pregnant than a sire with the lower EPD.

EPDs and accuracies for 533 sires meeting the listing criteria can be downloaded into a spreadsheet format and sorted as desired. Breeders may also request a printed version of the report if needed, by contacting the Performance Programs Department at 816-383-5100.

Click here to view sires.