Table 6.
Variance in feedlot DMI, RFI, and MEI and the incremental percentage of variation explained by selected traits1 within physiological categories after attributing variation explained by the preceding traits, the cumulative percentage of variation explained, and the percentage of variance unexplained. Data is for 59 Angus steers and heifers2 bred to vary in genetic merit for postweaning RFI
| Category and trait | Incremental and (cumulative) variation in DMI | Incremental and (cumulative) variation in RFI | Incremental and (cumulative) variation in MEI |
|---|---|---|---|
| Variance, kg/d or MJ/d | 1.24 | 0.67 | 129 |
| BW and gain | |||
| Midtest BW0.75, kg | 44.7%*** (44.7%) | — | — |
| ADG, kg/d | 1.4%ns (46.1%) | — | — |
| Body composition | |||
| End RIBFAT, mm | 18.3%*** (64.4%) | 32.7%*** (32.7%) | — |
| Midtest Protein, MJ | — | — | 22.6%*** (22.6%) |
| Midtest Fat, MJ | — | — | 39.7%*** (62.3%) |
| Movement | |||
| Feeder visits, visits/d | 5.7%** (70.0%) | 11.7%** (44.4%) | — |
| Activity test, MJ/d | — | — | 0.0%ns (62.3%) |
| Temperament | |||
| Flight speed, m/s | 0.0%ns (70.1%) | 0.0%ns (44.4%) | 0.6%ns (62.9%) |
| Digestive function | |||
| DMD, % | 2.4%* (72.5%) | 3.6%† (48.0%) | 2.6%† (65.5%) |
| Hematology | |||
| WBC, counts | 2.1%* (74.6%) | 3.7%* (51.7%) | 2.8%* (68.3%) |
| Immune competence | |||
| CIR test, mm | 1.6%† (76.2%) | 3.1%† (54.8%) | 1.4%† (70.1%) |
| Heat production | |||
| Unfed HP-WT, kg | 1.1%ns (77.3%) | 2.0%ns (56.8%) | 0.4%ns (71.5%) |
| Variance unexplained, % | 22.7% | 43.2% | 28.5% |
1Within categories, the trait with the strongest significant correlation with feedlot DMI was selected – see Tables 1 to 4.
2Comprising 29 steers and 30 heifers.
RFI = residual feed intake; MEI = ME intake; End RIBFAT = subcutaneous fat depth at the 12th/13th rib at the end of the RFI test; DMD = digestibility of DM; WBC = white blood cell; CIR test = cellular immune response relative to saline control in response to vaccine injection; HP-WT = heat production divided by BW.
ns P > 0.1; †P ≤ 0.1; *P < 0.05; **P < 0.01; ***P < 0.001.