Table 1.
Effects of days-in-milk on milk performance and blood biochemical parameters.
| Item | Days in Milk | SEM 1 | p-value | |||
|---|---|---|---|---|---|---|
| 90–119 (n = 53) |
120–149 (n = 74) |
150–179 (n = 57) |
180–219 (n = 103) |
|||
| Milk performance | ||||||
| Milk yield, kg/d | 36.0 a | 33.9 ab | 31.7 b | 32.4 b | 0.336 | <0.001 |
| Milk protein, % | 2.89 b | 3.08 a | 3.13 a | 3.14 a | 0.015 | <0.001 |
| Milk protein yield, kg/d | 1.04 | 1.04 | 0.99 | 1.01 | 0.009 | 0.351 |
| Milk urea nitrogen, mg/dL | 13.4 c | 13.8 bc | 14.5 ab | 14.8 a | 0.116 | <0.001 |
| Somatic cell counts, ×103/mL | 170 bc | 168 c | 284 a | 244 ab | 14.474 | <0.001 |
| Serum biochemical parameters | ||||||
| Blood urea nitrogen, mmol/L | 3.97 b | 3.70 c | 4.33 a | 4.47 a | 0.049 | <0.001 |
| Total protein, g/L | 66.6 a | 66.7 a | 62.7 b | 59.2 c | 0.440 | <0.001 |
| Albumin, g/L | 37.7 | 39.3 | 37.6 | 38.8 | 0.303 | 0.190 |
| Glucose, mmol/L | 3.94 c | 4.28 b | 4.49 ab | 4.73 a | 0.046 | <0.001 |
| NEFA, mmol/L 2 | 0.22 b | 0.17 c | 0.21 b | 0.26 a | 0.005 | <0.001 |
| Total cholesterol, mmol/L | 6.01 | 6.09 | 5.71 | 6.18 | 0.067 | 0.090 |
| β-hydroxybutyrate, mmol/L | 0.55 a | 0.49 ab | 0.46 b | 0.49 b | 0.008 | 0.006 |
| Triglyceride, mmol/L | 0.29 | 0.31 | 0.29 | 0.29 | 0.005 | 0.354 |
| Creatinine, μmol/L | 56.4 b | 56.7 b | 62.2 a | 62.5 a | 0.685 | <0.001 |
| Total bilirubin, μmol/L | 3.92 b | 4.08 b | 4.71 a | 4.93 a | 0.061 | <0.001 |
| Malonaldehyde, nmol/mL | 5.00 a | 4.72 a | 3.29 b | 3.64 b | 0.091 | <0.001 |
| Superoxide dismutase, U/mL | 136 | 135 | 136 | 136 | 0.796 | 0.833 |
| Glutathione peroxidase, U/mL | 128 ab | 131 ab | 134 a | 126 b | 1.098 | 0.038 |
| T-AOC, U/mL 3 | 4.01 a | 3.52 b | 3.42 b | 3.54 b | 0.050 | 0.001 |
| Parity | 2.92 | 3.16 | 3.00 | 3.01 | 0.066 | 0.619 |
1 SEM: Standard error of mean. 2 NEFA: Non-esterified fatty acids. 3 T-AOC: Total antioxidant capability. a,b,c Means within a row with different superscripts significantly differ (p < 0.05).