Gene editing in breeding

Leveraging advanced reproductive technologies to advance maternal and terminal breeding objectives in commercial beef cattle herds

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Abstract

Beef cattle operations aiming to retain replacement females and produce terminal pounds can accelerate genetic progress by decoupling terminal and maternal breeding objectives. This is particularly challenging in small herds where only one or two bulls may be deployed. Advanced reproductive technologies, such as fixed-time artificial insemination (FTAI) and sexed semen, provide opportunities to simultaneously pursue segmented terminal and maternal breeding objectives, especially in small and medium-sized operations. We explored the practical implementation and simulated genetic outcomes of a breeding system that deployed maternal sexed semen (~60%) and terminal semen (40%) & cleanup bulls in a FTAI protocol aimed at intentionally creating AI-sired replacements while maximizing terminal value in the remainder of the herd. We refer to this approach as 60/40 Synch. A large-scale breeding trial at the Bair Ranch Trust (Martinsdale, Montana, USA) implemented 60/40 Synch and a control FTAI program over a three-year period in a commercial Simmental x Angus cowherd (N = 1,574). In this study, the 60/40 group had fewer AI-sired calves (P < 0.001), yet the percentage of AI-sired females remained the same (P = 0.996). When compared to the control group, the 60/40 group had a significantly lower 21-day calving rate (P < 0.001), however 42-day calving rate only tended to be lower (P = 0.057) and total calving rate did not differ (P = 0.52). To assess the long-term genetic and phenotypic outcomes associated with decoupling maternal and terminal breeding objectives, we implemented a range of stochastic breeding program simulations through AlphaSimR, a software designed for modelling long-term genetic change in breeding programs. Three simulated seedstock populations were selected based on maternal, terminal, and all-purpose economic selection indexes designed in iGENDEC for use in commercial populations deploying conventional (All-Purpose) and 60/40 Synch breeding schemes (Maternal & Terminal). Genetic progress was measured in both commercial replacement females and feeder calves over a twenty-year period. Commercial populations made similar genetic progress in key maternal traits due to the low heritability of fertility traits and low selection accuracy and intensity of replacement females in standard commercial beef operations. Terminal progress was significantly greater in the 60/40 feeder calf population due to the high heritability of growth and carcass traits which make up terminal selection indexes. Future work should include simulating the non-additive effects generated through crossbreeding in the 60/40 Synch program, which is expected to substantially increase the phenotypic expression of lowly heritable reproductive traits in replacement females. This work serves as a significant demonstration of the value of separating maternal and terminal objectives in cattle breeding programs, and a practical approach to implementation.

Keywords: 2026

How to Cite:

Ulmer, J., Wells, K. & Rowan, T., (2026) “Leveraging advanced reproductive technologies to advance maternal and terminal breeding objectives in commercial beef cattle herds”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286922. doi: https://doi.org/10.31274/wcgalp.24166

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