Table 5.
Effect of dietary CP level on milk N secretion, and N excretion in feces and urine.
| Dietary CP Content, g/kg DM | p-Value | |||||||
|---|---|---|---|---|---|---|---|---|
| 141 | 151 | 177 | 201 | SEM | Diet | Linear | Quadratic | |
| Total N intake, g/day | 436 b | 457 b | 637 a | 633 a | 21.1 | <0.0001 | <0.0001 | 0.015 |
| Urinary excretion | ||||||||
| Urine output, kg/day | 18.5 b | 18.6 b | 24.7 a | 24.1 a | 0.978 | <0.0001 | <0.0001 | 0.054 |
| Urinary N, g/day | 146 c | 156 c | 243 b | 287 a | 13.8 | <0.0001 | <0.0001 | 0.652 |
| Urinary N, % N intake | 33.7 b | 35.0 b | 38.7 a,b | 45.6 a | 2.58 | 0.008 | 0.001 | 0.501 |
| Fecal excretion | ||||||||
| Fecal DM output, kg/day | 5.61 | 5.23 | 6.39 | 5.7 | 0.275 | 0.051 | 0.174 | 0.119 |
| Fecal N, g/day | 185 b | 175 b | 234 a | 193 b | 11.8 | 0.016 | 0.110 | 0.023 |
| Fecal N, % N intake | 42.2 a | 38.7 a,b | 36.7 b | 30.2 c | 1.55 | <0.0001 | <0.0001 | 0.551 |
| Manure N, g/day | 331 b | 332 b | 480 a | 481 a | 22.7 | 0.0002 | <0.0001 | 0.116 |
| Manure N, % N intake | 75.7 | 73.7 | 75.5 | 75.8 | 3.19 | 0.948 | 0.806 | 0.836 |
| Milk N secretion | ||||||||
| Milk N 1, g/day | 127 b | 138 a,b | 161 a | 149 a,b | 7.68 | 0.033 | 0.022 | 0.048 |
| Milk N, % N intake | 29.6 a | 29.9 a | 25.5 a,b | 23.3 b | 1.62 | 0.021 | 0.003 | 0.953 |
1 Determined as milk protein yield/6.38; SEM, standard error of least square means; a,b,c least square means in the same row with different superscript letters differ (p < 0.05).