August 2026 NEBRASKA CATTLEMAN 31 are characterized by a high proportion of unsaturated fatty acids, and soybean oil contains approximately 50 percent linoleic acid. Compared with tallow, vegetable oils have greater potential to modify rumen fermentation. Therefore, cattle may not respond the same if vegetable oil directly replaces tallow or yellow grease. Even fat sources low in unsaturated fatty acids such as tallow may have detrimental impacts to rumen health at high inclusion levels. The optimal inclusion of supplemental fats or oils in feedlot diets has both biological and economic implications. To assess responses across fat source and inclusion level, we reviewed 35 published studies that evaluated supplemental fat in feedlot diets from animal fat, restaurant grease and seed oils. Using a meta-analysis approach, we evaluated animal performance responses when supplemental fat was included up to 6 percent of diet dry matter. As expected, supplemental fat generally reduced dry matter intake, allowing cattle to consume less feed while maintaining similar or greater energy intake. The result was usually improved feed conversion. Animal fats, particularly tallow, produced the most consistent improvements in average daily gain when included at moderate concentrations. The largest responses occurred when supplemental fat represented approximately 3 to 4 percent of diet dry matter. Beyond that level, responses tended to plateau or decline. Seed oils also improved feed efficiency, but their optimum inclusion appeared to occur at slightly lower concentrations, perhaps closer to 2 to 3 percent of diet dry matter. Thus, feedlots may need to consider lower inclusion rates when feeding vegetable oils compared with tallow or yellow grease. In today’s market conditions, carcass weight drives profitability. While supplemental fat is most recognized for improving feed efficiency, it can also increase carcass weight by 10 to 20 pounds. With relatively cheap corn and historically strong fed-cattle prices, a typical cost-of-gain calculation may not capture the full value of supplemental fat if it ignores added carcass weight. In the current market, supplemental fat should be viewed less as a feed-efficiency tool and more as a source-specific investment that must return value through both improved feed conversion and heavier carcasses. ~NC~ For feedlots, the question is no longer simply whether fat improves performance, but whether the performance response is large enough to pay for a higher priced ingredient.
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