The ability to rebreed for a second calf given that a heifer had her first calf as a two-year-old may be influenced by the animal's ability to continue to grow to maturity and still conceive. As of this writing one beef cattle organization, the American Gelbvieh Association (AGA), produces an EPD for PG30.
Binary observations for PG30 of 0 or 1 are assigned to those females who have a successful calving from being bred for the first time to calve as a two-year-old (HPG). If a female with a successful HPG observation recorded a calf from being bred a second time to calve as a three-year-old, she is assigned a successful PG30 observation (1). If a female with a successful HPG observation fails to record a calf from being bred a second time to calve at three years of age, she is assigned an unsuccessful PG30 observation (0).
No adjustments are available for PG30
Contemporary group is formed by the concatenation of yearling herd/workgroup and year of birth. Observations on females who are transferred between first and second calves should be eliminated from the PG30 contemporary group, or regrouped if numbers are sufficient.
The AGA PG30 EPD is produced using a single-trait linear pedigree BLUP animal model that includes contemporary group, percent Gelbvieh and percent expected heterozygosity as fixed effects.
Observations from contemporary groups with no variation (all 1's or all 0's) are eliminated in the AGA analysis. However, this may not be necessary unless a maximum a posteriori threshold model is used, which requires variation in contemporaty group when fit as a fixed effect for singularity.
Currently, there is no peer-reviewed literature describing the methods used for the AGA evaluation.
Information in the article was derived from a report produced for the AGA by Scott Speidel and Mark Enns, Colorado State University, Fort Collins; Additional information came from a report by Mike MacNeil, Delta G.