Table 4.
Effect of dietary CP level on milk yield, components, and milk components yield.
| Dietary CP Content, g/kg DM | SEM | p-Value | ||||||
|---|---|---|---|---|---|---|---|---|
| 141 | 151 | 177 | 201 | Diet | Linear | Quadratic | ||
| Milk yield | ||||||||
| Milk, kg/day | 23.7 b | 24.5 b | 28.6 a | 25.3 a,b | 1.29 | 0.048 | 0.153 | 0.044 |
| 4% FCM, kg/day | 25.6 | 26.6 | 31.1 | 28.1 | 1.56 | 0.094 | 0.114 | 0.079 |
| Milk/DIM | 1.27 | 1.29 | 1.28 | 1.28 | 0.072 | 0.997 | 0.969 | 0.868 |
| FCM/DIM | 1.37 | 1.40 | 1.40 | 1.41 | 0.082 | 0.987 | 0.754 | 0.920 |
| Milk components | ||||||||
| Fat, g/kg | 45.6 | 45.9 | 45.5 | 47.5 | 0.779 | 0.254 | 0.121 | 0.252 |
| Lactose, g/kg | 47.8 | 47.9 | 47.7 | 48.3 | 0.600 | 0.910 | 0.682 | 0.627 |
| Protein, g/kg | 34.1 c | 34.8 b,c | 37.2 a,b | 37.5 a | 0.834 | 0.023 | 0.004 | 0.359 |
| Casein, g/kg | 27.1 b | 28.1 a,b | 28.7 a | 29.3 a | 0.475 | 0.029 | 0.005 | 0.445 |
| Urea-N, mg/kg | 105 c | 110 c | 189 b | 205 a | 4.04 | <0.0001 | <0.0001 | 0.003 |
| Milk components yield | ||||||||
| Fat yield, kg/day | 1.09 | 1.16 | 1.22 | 1.21 | 0.059 | 0.383 | 0.151 | 0.323 |
| Lactose yield, kg/day | 1.15 | 1.23 | 1.28 | 1.23 | 0.060 | 0.493 | 0.367 | 0.212 |
| Protein yield, kg/day | 0.81 | 0.89 | 0.99 | 0.96 | 0.049 | 0.061 | 0.022 | 0.116 |
| Casein yield, kg/day | 0.64 | 0.72 | 0.77 | 0.75 | 0.032 | 0.051 | 0.028 | 0.070 |
| Urea-N yield, g/day | 2.52 b | 2.99 b | 5.05 a | 5.22 a | 0.233 | <0.0001 | <0.0001 | 0.007 |
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).