135. Effect of RFI and RNE on Energy Partitioning in Beef Cows During Gestation and Lactation

Abstract This study evaluated how residual feed intake (RFI) and residual net energy retained (RNE) classifications influence energy partitioning in crossbred Angus beef cows consuming an unprocessed forage diet during gestation and lactation. Cows were retrospectively classified as efficient, moderate, or inefficient for RFI and RNE within each physiological stage. RFI classification significantly affected energy allocation to maintenance, with inefficient cows partitioning more metabolizable energy to maintenance (gestation: P < 0.01; lactation: P = 0.02) than moderate or efficient cows. Conversely, RNE-efficient cows allocated more net energy to tissue accretion during both gestation and lactation (P ≤ 0.05), reflecting greater capacity for energy retention. The relationship between RFI and RNE was weak during gestation (R² = 0.13) and negligible during lactation (R² = 0.06). These results highlight that RFI and RNE capture distinct but complementary aspects of energy utilization in beef cows and that selection for either trait can differentially influence the efficiency of energy partitioning across physiological stages.