Increased product demand accompanied by a simultaneous reduction in resources has put pressure on livestock producers to improve feed efficiency. Residual feed intake (RFI) is one of many tools used to quantify feed efficiency and is defined as the difference between observed feed consumption and predicted consumption based on performance. Residual feed intake assists in identification of animals that convert consumed energy into energy of product more efficiently than contemporaries. Use of modern selection tools will enable more rapid advancements in feed efficiency; however, it is important that cows that are efficient under current conditions are also efficient when subjected to conditions of the future. Furthermore, there are likely physiological and metabolic mechanisms that differ among high and low efficiency cows. Four separate experiments were conducted to determine the repeatability of RFI across high and low starch diets as well as the relationship between digestive efficiency and RFI. Additionally, the relationships between RFI and blood metabolites that are indicators of carbohydrate metabolism and energy partitioning were studied. We determined that RFI was highly repeatable across high and low starch diets, and that digestibility may account for some variation in RFI. We conclude that cows that are efficient when fed diets common at present will probably also be efficient when fed diets in the future that will likely be higher in byproduct type feeds.
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