283 Managing carcass outcomes through lifetime energy supply in beef cattle.

Abstract The North American cattle industry is considered the “Gold Standard” for intensive beef production worldwide due to its competitive and resilient systems. Its broad geographical distribution from north to south and east to west creates natural safeguards against weather disasters, diseases, and unpredictable events that could negatively impact production. Unlike other regions, North America is better equipped to handle political and societal pressures, thanks to adaptable infrastructure and resource availability. The region boasts ideal conditions for beef production. Grazing lands in the Southern and Western U.S. support the cow herd, while the Midwest produces crops that feed both young and finishing cattle. Abundant grain supplies and high-quality feeder cattle from a productive cow herd contribute to the competitiveness of North American cattle feeding systems. Economical weight gain is supported through a mix of grazed forage, harvested forages, and by-products during both the growing (backgrounding) and finishing phases. Efficient transportation networks like rivers, railroads, and highways allow corn from crop-producing areas to be easily shipped to cattle feeding regions. Current market trends favor heavier carcasses and longer durations on high-energy finishing diets. However, the long-term effects of feeding native beef cattle ad libitum for over 300 days on diets exceeding 1.39 Mcal/kg NEg are not fully understood. Extended use of corn-milling co-products may pose risks, such as cumulative sulfur exposure. There is also concern about whether cattle physiology can support continuous carcass growth, as organs and muscle tissues may not develop at the same rate. Two potential management strategies to reduce time on high-energy diets include: 1) extending the backgrounding period or 2) applying limit- or program-feeding methods before transitioning to finishing diets. These approaches may help reduce digestive issues and mortality during late feeding periods. Limit-feeding restricts intake below what cattle would eat freely, while program feeding calculates feed needs based on energy required for maintenance and targeted weight gain, using the California Net Energy System. The purpose of the talk will be to highlight on-going research conducted at South Dakota State University and other North American Institutions related to enhancing economic returns of modern cattle that produce heavier carcasses with greater quality grade potential than the previous 25 y.