Table 4. Effects of dietary CP levels or oscillating dietary CP on ruminal nitrogen metabolism in dual-flow continuous culture system.
| Item1 | Treatment, CP% | SEM | P-value | |||||
|---|---|---|---|---|---|---|---|---|
| 10% | 12% | 14% | OSC | 12% vs. OSC | Linear | Quadratic | ||
| NH3-N, mg/100 mL | 2.9 | 3.1 | 8.9 | 4.8 | 1.10 | 0.12 | <0.01 | <0.01 |
| CP digestibility, % | 77.5 | 70.0 | 67.0 | 68.4 | 7.43 | 0.86 | 0.30 | 0.79 |
| Nitrogen flow, g/d | ||||||||
| Total N | 1.8 | 2.0 | 2.1 | 1.8 | 0.15 | 0.27 | 0.30 | 0.81 |
| NH3-N | 0.1 | 0.1 | 0.3 | 0.1 | 0.03 | 0.11 | <0.01 | <0.01 |
| NAN | 1.8 | 1.9 | 1.8 | 1.9 | 0.09 | 0.70 | 0.72 | 0.24 |
| Microbial N | 0.9 | 1.1 | 1.0 | 1.1 | 0.04 | 0.78 | 0.06 | 0.01 |
| Microbial efficiency2 | 31.3 | 40.5 | 37.4 | 36.5 | 2.20 | 0.19 | 0.05 | 0.02 |
| RDP supply, g of N/d3 | 0.8 | 1.1 | 1.2 | 1.1 | 0.07 | 0.84 | <0.01 | 0.34 |
| RUP flow, g of N/d4 | 0.9 | 0.9 | 1.0 | 0.9 | 0.07 | 0.95 | 0.27 | 0.34 |
1NH3-N = ammonia nitrogen; CP = crude protein; NAN = non-ammonia nitrogen; OM = organic matter.
2Microbial efficiency = g of microbial N/kg of DM truly digested.
3RDP supply = rumen-degraded protein supply = total N flow–microbial N. [28]
4RUP flow = rumen-undegraded protein flow = total N intake–RUP flow. [28]