16 Genetic Parameter Estimates for Age at First Calving in Simmental and Red Angus Heifers

Abstract The objective of this study was to determine genetic parameter estimates for age at first calving (AFC) in Red Angus and Simmental heifers. ability a heifer calve earlier has implications on calf performance the heifer's successive re-breeding. Heifer pregnancy data were obtained from International Genetic Solutions, where females with exposure records included population. Females subsequent record between 630 810 days analysis. embryo transfer or multiple birth progeny excluded. Records single-animal contemporary groups no variation eliminated after filtering, there 149,379 mean breed proportion 0.58 ± 0.25, 83,191 0.80 0.13. A 3-generation pedigree file containing 291,530 animals 25,585 unique sires 161,921 dams, 174,914 19,733 99,464 dams used separate AFC 724.8 28.64 d, 724.2 29.93 respectively. Data each modeled separately using single trait animal model random additive residual effects, fixed effect group ASReml 3.0. Contemporary defined as breeder, herd, year born, yearling group. additive, residual, phenotypic variances 120.08, 520.37, 640.45 d2, For Angus, 85.67, 543.56, 629.24 d2 variances, heritability 0.19 0.0059 0.14 0.0076, These results demonstrate is lowly moderately heritable. Lower higher variance compared may suggest population larger underlying fertility influences such puberty. breeding values 6.1 8.0, minimum -24.4 maximum 54.7. Whereas resulted 4.0 5.6 -16.1, 37.3, comparable estimates, low standard error, range selection improved can be attained. It worth further exploring impact effects heterosis calving. While does not account heifers that did their year, tandem should heavily emphasized due economic importance both traits.