84. Impacts of Trait Selection Pressures in Angus Cows on Female Productivity.

Abstract

Growth traits, that ultimately boost weaning and yearling weights, are highly heritable. However, they also increase mature cow weights and can increase input costs in cow-calf operations. Thus, optimal production in beef cattle operations depends on balancing growth with maternal traits and environmental limitations, like forage availability, to ensure overall system efficiency. The objective of this study was to evaluate the impacts of trait selection pressures over time in Angus cattle and compare these outcomes with selection trends in the national Angus herd. Records from the Angus cow-calf herd at The Pennsylvania State University (PSU) were collected from 1992 to 2024 (n = 1,547). National averages and estimated progeny differences (EPDs) for the traits of interest were compared across time to understand variations in selection pressures. These data were analyzed using the PROC MIXED procedure of SAS 9.4. Over time, the PSU herd exhibited a gradual increase in mature cow weight (MW) EPD (R² = 0.33), and remained at or above national averages until 2012, after which PSU herd remained below the national population. In addition, mature height (MH) EPDs declined and remained below national averages. The birth weights (BW) decreased by 0.19 kg/year P < 0.0001) in the PSU herd, aligning this herd with national BW averages by 2023. Although weaning weight (WW) EPDs increased over time, reduced selection pressure after 2013 coincided with a decline in phenotypic WW (P < 0.0001). These trends support intentional moderation of cow size. However, lighter PSU cows do tend to wean a greater percentage of their body weight (P < 0.0001), a metric suggesting improved production efficiency with decreasing cow size. Management of the PSU herd shifted after 2013 and altered management trends suggest an interesting dichotomy between individual management pressures and national EPD trends. Ultimately, despite national trends, trait selection should be centered within a herd and around the environment, management, and goals of the specific operation.