Estimating the Value of Including Resilience in a Multi-Trait Selection Index Designed for Australian Merino Sheep.

General resilience in livestock can be estimated from the variability in longitudinal data and may support balanced breeding objectives by helping animals better cope with environmental stress. However, its economic value and inclusion within multi-trait selection indexes remain largely unexplored. Current genetic improvement programs for sheep primarily focus on wool growth, reproduction and lean meat production. This study developed a bioeconomic model to estimate the economic value of general resilience, using the natural logarithm of variance of wool fibre diameter as a resilience indicator trait in sheep. A commercial Merino sheep enterprise was considered, and the economic value of resilience was derived from its association with health, mortality, and energy allocation for production. The breeding objective included key traits related to meat production, reproduction, and wool quality and quantity, to compare the economic impact of resilience with these traits. Among 13 traits, resilience contributed 2.02% to the total value of the index and ranked 11th in economic importance. After 10 years of simulated selection, resilience was expected to improved by 0.07 genetic standard deviations, translating to a modest economic gain of $0.08 per ewe. A sensitivity analysis was conducted to assess the impacts of increasing the relative contribution of resilience within the index on selection responses under four scenarios: (i) base genetic correlations, (ii) stronger correlations, (iii) weaker correlations, and (iv) adding genomic information. Resilience responded 50%-75% more effectively to selection when it had stronger genetic correlations with production traits or when genomic information was incorporated. However, placing greater emphasis on resilience (> 10% of the index) reduced progress in key production traits. Future research should explore these trade-offs in industry selection indexes to integrate resilience effectively without compromising productivity.