Comparison and relation among different estimates of residual feed intake for Japanese Black (Wagyu) bulls

Residual feed intake (RFI) was estimated by ordinary regression (RFI_ord), linear regression (RFI_reg), and genetic regression (RFI_gen) for Japanese Black bulls, and compared among them by the magnitude of correlations, heritabilities, and empirical mean squared errors. The estimations were made for a total test periods of 140 days (77 bulls) and 112 days (663 bulls) sub‐divided each into two equal stages: first half and second half of the test periods. The means of RFI_reg, RFI_ord, and RFI_gen for the total test periods were 1.09, ?0.05, and ?2.21 kg/day, respectively. The genetic variation exists for these estimates at different stages of the test period. High genetic and phenotypic correlations (>0.95) were found between RFI_ord and RFI_gen, confirming that these are regarded practically as the same traits. The phenotypic variance (0.714) and heritability (0.24) of RFI_ord were close to those of RFI_gen (0.726 and 0.25, respectively). According to the empirical mean squared errors from the result of the total test periods, RFI_gen yielded better estimates of RFI. The high to moderate heritabilities for RFI_ord were estimated for the three stages of the test periods, indicating that RFI_ord might be an alternative estimate for genetic improvement of feed utilization.