Technical note: do dietary net energy values calculated from performance data offer increased sensitivity for detecting treatment differences?

A simulation technique involving 100 hypothetical experiments (24 pens each for control and treated groups) for each of 3 cases was used to evaluate the statistical sensitivity of dietary NE concentrations calculated from performance data. In case 1, the treated population had a 12-kg increase in mean shrunk final BW (FBW) and no change in DMI; in case 2, the treated population had a 19-kg increase in mean shrunk FBW and 0.25-kg increase in DMI; and in case 3, the treated population had a 0.43-kg decrease in DMI and no change in ADG. In all 3 cases, cattle were assumed to be fed for 150 d, and changes in the treated group resulted in a similar increase in G:F (approximately 5%). Population means and SD for initial and final BW and DMI were used to generate 100 experiments based on normal distribution equations, and resulting BW and DMI values were used to calculate dietary NE(m) and NE(g) concentrations required to yield the observed performance. The BW, ADG, DMI, G:F, and NE values for control and treated samples were statistically compared within each experiment, with significance declared at P <or= 0.05. In case 1, FBW differed in 96% of the experiments, whereas the DMI and ADG differed in 3 and 87% of the experiments, respectively. The G:F differed (P <or= 0.05) in 63% of the experiments, but NE concentrations differed in only 42% of the experiments. In case 2, FBW differed between control and treatment in 100% of the experiments, whereas DMI and G:F differed in 53 and 52% of the experiments, respectively. Similar to FBW, ADG was greater for treated pens in 100% of the experiments, but dietary NE values differed in only 23% of the experiments. In case 3, FBW differed in 3%, DMI differed in 91%, and ADG differed in 3% of the experiments. In contrast to results with cases 1 and 2, differences in G:F were observed in 55% of the experiments compared with differences in 78% of the experiments for calculated NE values. These data suggest that the performance variable that drove changes in NE values (e.g., DMI or changes in BW) was a more sensitive measure of treatment effects than calculated NE dietary values. Dietary NE values calculated from performance data can be useful for describing treatment effects, but they do not generally seem to offer statistical advantages in sensitivity over the performance variables from which they are derived.