Lay Summary Improving how efficiently beef cows use their feed is vital for sustainable and profitable cattle production. This study examined intake, maintenance energy requirements, residual feed intake (RFI) and residual net energy recovered (RNE), in crossbred Angus beef cows fed a forage diet during gestation and subsequent lactation. Key animal performance and metabolic traits were measured and used to calculate efficiency indexes. Results showed that cows classified as RFI-efficient consistently ate less forage without sacrificing body weight, condition, or milk output, both while pregnant and nursing, in addition to allocating less energy to maintenance. Cows ranked as RNE-efficient directed more net energy to maternal tissue accretion and less energy to maintenance. Methane emissions per kilogram of feed were significantly higher in the RFI-efficient group at gestation but not at lactation. Interestingly, the efficiency rankings of individual cows tended to change between pregnancy and nursing, suggesting that feed and energy efficiency are not fixed traits across production stages. In contrast, feed intake and maintenance energy requirements are more persistent across stages of production.
Garcia-Ascolani et al. (Mon,) studied this question.