Using the difference in actual and expected calf liveweight relative to its dam liveweight as a statistic for interherd and intraherd benchmarking and genetic evaluations1.

The importance of improving the efficiency of beef production systems using both genetic and management strategies has long been discussed. Despite the contribution of the mature beef herd to the overall cost of production in the sector as a whole, most strategies for improving (feed) efficiency have focused on the growing animal. The objective of the present study was to quantify the phenotypic and genetic variability in several novel measures that relate the weight of a calf to that of its dam and vice versa. Two novel residual traits, representing the deviation in calf weight relative to its expectation from the population based on its dam's weight (DIFFcalf) or the deviation in the weight of the dam relative to its expectation from the population based on its calf's weight (DIFFdam), were calculated while simultaneously accounting for some nuisance factors in a multiple regression model. Four supplementary traits were also calculated, namely, 1) the deviation in calf weight from its expectation expressed relative to the weight of the dam (DIFFcalf_ratio), 2) the deviation in dam weight from its expectation relative to the weight of the dam (DIFFdam_ratio), 3) DIFFcalf-DIFFdam, and 4) the simple ratio of calf weight to its dam's weight (RATIOcalfdam). Genetic and residual variance components for each of the 6 traits were estimated using animal-dam linear mixed models. The phenotypic SD for DIFFcalf was 42 kg and, when expressed relative to the weight of the dam (i.e., DIFFcalf_ratio), was 0.07. The genetic SD for DIFFcalf and DIFFcalf_ratio was 16.66 kg and 0.02, respectively. The direct and maternal heritability estimated for DIFFcalf was 0.28 (SE = 0.04) and 0.11 (SE = 0.02), respectively, and for DIFFcalf_ratio was 0.24 (SE = 0.04) and 0.17 (SE = 0.03), respectively. The genetic SD for DIFFdam was 47.09 kg; the direct heritability was 0.50 (SE = 0.03), and the dam repeatability was 0.75 (SE = 0.01). The genetic SD for RATIOcalfdam was 0.03; the direct and maternal heritability was 0.24 (SE = 0.04) and 0.24 (SE = 0.03), respectively. The suggested traits outlined in the present study provide useful metrics for benchmarking dam-calf efficiency; in addition, the genetic variability detected in these traits suggest genetic progress for more efficient dam-calf pairs is indeed possible.