Correlations between purebred and crossbred body weight traits in Limousin and Limousin-Angus populations

The purpose of this study was to estimate correlations between purebred and F-1 crossbred performance to verify the appropriateness of current models used in multibreed selection. Records on birth weight (WB) and weaning weight (WW) from purebred Limousins (LIM) and Limousin x Angus progeny (F-1) were used to estimate genetic parameters using a multiple-trait (purebred and F-1 weights were different traits) approach. For WB, there were 148,647 records for LIM and 17,981 for F-1, and for WW, there were 81,585 records for LIM and 21,778 for F-1. The fixed effect in models for LIM and F-1 animals was contemporary group. Random effects for LIM animals were direct genetic, maternal genetic, and maternal permanent environment effects. Random effects for F-1 were sire and dam. The pedigree for Angus dams used for crossing was unavailable and therefore these dams were assumed unrelated. The direct h(2) estimates (SE) for purebred animals were 0.41 (0.05) and 0.24 (0.02) for WB and WW, respectively. For F-1, the same estimates were 0.22 (0.09) and 0.32 (0.05). Genetic correlations estimates between purebreds and crossbreds were 0.84 (0.07) and 0.64 (0.18) for WB and WW, respectively. The genetic correlation for WW estimated in this study suggests that F-1 and purebred information for this trait should not be treated, genetically, as the same trait due to different genetic effects molding it. However, the genetic correlation for WB was much higher, indicating that this trait in purebreds and F-1 is essentially the same trait.