Genetic analysis of feed efficiency in calves and first-lactation Holstein cows

Feed efficiency is a critical trait in dairy cattle production, with profound implications on both economic profitability and environmental sustainability. The objective of this study was to assess genetic relationships between feed intake and feed efficiency traits of calves and first-lactation Holstein cows. Data from 795 calves and 720 primiparous cows were analyzed, with feed intake measured as metabolizable energy intake (MEI) in calves and DMI in cows. Calf MEI was summarized as weekly averages across 2 key developmental phases: wk 1 to 3 (MEI1) and wk 7 to 9 (MEI2). Dry matter intake was recorded weekly from lactation wk 9 to 44. Feed efficiency was defined as residual feed intake (RFI) in primiparous cows and residual metabolizable energy intake (RMEI) in calves, estimated for the same 2 developmental periods as MEI (RMEI1 and RMEI2). In both cases, efficiency was expressed as the deviation of observed intake from expected intake based on energy sinks. Using a multitrait repeatability model, genetic correlations were estimated among the 6 traits (MEI1, MEI2, RMEI1, RMEI2, DMI, and RFI). Notably, genetic correlations (±SE) were moderate and positive between MEI2 and DMI at 0.49 ± 0.15 and RFI at 0.44 ± 0.21. In contrast, the genetic correlations of MEI1 with DMI was 0.15 ± 0.15 and RFI was 0.12 ± 0.21, which were close to zero and not significant. The genetic correlation between RFI and RMEI1 was estimated at -0.35 ± 0.26, indicating a possible negative relationship, although not significant. A moderately high positive genetic correlation was estimated between RFI and RMEI2 at 0.71 ± 0.36. These findings suggest that RMEI2 seems to be favorably genetically correlated with RFI, whereas RMEI1 shows no or perhaps a relatively weak unfavorable association with RFI. The results likely reflect physiological differences in calf rumen development, but support the potential for early selection based on RMEI2 to enhance cow feed efficiency.