Development of economic selection indexes for beef-on-dairy systems and implication for sire re-ranking in U.S....

The rapid expansion of beef-on-dairy (B×D) crossbreeding in the United States has increased the need for selection tools tailored to this unique production system. The objectives of this study were to develop economic selection indexes specific to B×D systems under U.S. conditions and to evaluate the extent of sire re-ranking relative to conventional beef-on-beef (B×B) indexes. The current study utilized iGENDEC, a web-based decision support platform hosted by the Beef Improvement Federation. iGENDEC enables users to enter enterprise-specific information related to breeding goals, breeding systems, economic costs/returns, and current phenotypic performance. Using stochastic simulation, iGENDEC creates a simulated population informed by the user's parameters to enable calculation of the marginal economic value of each trait in the specified breeding objective. Using iGENDEC, economic selection indexes were constructed for multiple crossbreeding scenarios incorporating traits related to carcass merit, feed intake, and calving performance. Beef bulls (n = 27,123) were evaluated to quantify differences in ranking across production systems and index assumptions. Results indicated that BxD systems placed greater economic emphasis on feed intake and hot carcass weight, while B×B systems placed more emphasis on carcass marbling. Despite strong Spearman rank correlations between indexes (average = 0.931), only 70.7% of the 100 top-ranked sires overlapped between B×D and B×B systems, indicating meaningful differences in sire selection. Differences in production assumptions, including carcass weight targets and days on feed, further influenced economic weights and selection outcomes. Opportunity costs associated with using B×B-based indexes in B×D systems averaged $3.24 per exposure with a maximum value of $8.26 per exposure. These findings demonstrate that even small differences in index construction can lead to suboptimal sire selection and reduced profitability. Consequently, selection indexes should be tailored to specific production environments to ensure alignment with economic drivers and to maximize genetic progress in beef-on-dairy systems.