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.

A performance database is assembled using available breeding information on first-calf heifers. A heifer's breeding record is coded as a success or failure of being pregnant, based on any pregnancy check data or calving information recorded and submitted by the breeder. Edited data on heifers are analyzed in a threshold analysis with a full animal model and three generation pedigree.

Use of Heifer Pregnancy EPDs

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. 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 1 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.

Figure 1. Heifer Pregnancy EPD example