Table 2.
Productivity of lactating cows selected for phenotypic divergence in residual feed intake (RFI)
| Items | Low RFI |
High RFI |
SEM | P valuea | ||
|---|---|---|---|---|---|---|
| RFI | Day | RFI × Day | ||||
| Number, head | 10 | 8 | ||||
| Lactation performanceb | ||||||
| DMI, kg/d | 24.2 | 26.6 | 0.68 | 0.02 | < 0.01 | 0.32 |
| Milk yield, kg/d | 34.0 | 33.1 | 1.39 | 0.65 | < 0.01 | 0.96 |
| Milk protein yield, kg/d | 1.11 | 1.10 | 0.05 | 0.90 | 0.03 | 0.91 |
| ECM, kg/d | 35.7 | 36.4 | 1.35 | 0.72 | < 0.01 | 0.85 |
| ECM/DMI, kg/kg | 1.48 | 1.36 | 0.03 | < 0.01 | < 0.01 | 0.77 |
| Milk/DMI, kg/kg | 1.41 | 1.24 | 0.04 | < 0.01 | < 0.01 | 0.64 |
| RFI, kg/d | −0.96 | 1.18 | 0.22 | < 0.01 | – | – |
| Milk compositionc | ||||||
| Milk fat, % | 3.83 | 4.23 | 0.12 | 0.01 | 0.05 | 0.87 |
| Milk protein, % | 3.26 | 3.33 | 0.06 | 0.40 | < 0.01 | 0.64 |
| Lactose, % | 4.97 | 4.90 | 0.03 | 0.21 | < 0.01 | 0.15 |
| Total solids, % | 12.7 | 13.0 | 0.14 | 0.12 | 0.12 | 0.90 |
| MUN, mg/dL | 12.7 | 13.9 | 0.39 | 0.05 | < 0.01 | 0.62 |
| SCC, × 103/mL | 50.5 | 38.7 | 9.46 | 0.39 | 0.33 | 0.46 |
| Days in milk | 193 | 182 | 6.30 | 0.22 | – | – |
| Parity | 2.70 | 2.50 | 0.22 | 0.56 | – | – |
| Body weight, kg | 739 | 737 | 16.7 | 0.96 | < 0.01 | 0.24 |
| Average dairy gain, kg | 0.17 | 0.26 | 0.18 | 0.66 | 0.08 | 0.68 |
aP value associated with RFI, time, and the interaction of RFI and time
bDMI, dry matter intake; ECM (kg) = 0.3246 × milk yield (kg) + 13.86 × milk fat (kg) + 7.04 × milk protein (kg) [44]. All cows remained pregnant during the trial
cMUN milk urea nitrogen, SCC somatic cell counts