1820
Short Term Feed Restriction Increases Afternoon but not Morning Milk Fat Concentration in Lactating Dairy Cows
The elevated milk fat concentration exhibited by cows during the early periparturient period is related to the degree of body tissue mobilization. We hypothesized that feed restriction could be used as tool to study temporal changes in milk composition. Our objective was to test the effect of short-term feed restriction on milk fat concentration. Ten multiparous Holstein cows (100 + 17 DIM) were used in the 21 d study. During d 1 to 14, all cows were allowed ad libitum access to a total mixed ration that was formulated to meet 2001 NRC nutrient requirements for 40 kg/d milk production and this period was used as covariate in the ANOVA. Treatments (Trt) consisted of either ad libitum (AL) or restricted (RES) feeding during d 15 to 18 where RES cows were fed 60% of their d 1 to 14 ad libitum intakes. All cows returned to ad libitum feeding on d 19 to 21. Cows were milked twice daily at 0630 and 1630 h and fed once daily at 0900 h. Milk production and composition were measured at each milking on d 13 to 21. As expected, milking time influenced milk production and composition (P < 0.001) for fat and protein. While feed restriction decreased (P < 0.001) milk production, but not milk protein and fat percent. There were treatment by milking time interactions for milk fat (P < 0.001) and protein (P = 0.008) percent which were increased at the 1630 h but not the 0630 h milking. A day by treatment by milking time interaction (P< 0.02) was observed for milk fat which showed the greatest elevation at the 1630 h milking on d 16. These results demonstrate that feed restriction can be used to study temporal changes in milk composition.
Milking: |
---- 0630 h ---- |
---- 1600 h ---- |
--------- P = -------- |
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Treatment |
AL |
RES |
AL |
RES |
SEM |
Time |
Trt |
Trt*Time |
Milk, kg |
21.6 |
19.2 |
18.8 |
15.2 |
0.72 |
0.007 |
0.001 |
0.014 |
Milk protein, % |
2.88 |
2.87 |
2.73 |
2.87 |
0.058 |
0.001 |
0.392 |
0.001 |
Milk other solids, % |
5.66 |
5.54 |
5.54 |
5.54 |
0.028 |
0.073 |
0.065 |
0.008 |
Milk Fat % |
||||||||
Day 15 |
2.98 |
2.69 |
4.32 |
4.10 |
0.24 |
0.001 |
0.274 |
0.001 |
Day 16 |
2.96 |
2.89 |
4.30 |
5.86 |
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Day 17 |
2.96 |
2.87 |
4.20 |
4.94 |
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Day 18 |
3.00 |
2.89 |
4.16 |
5.10 |
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Days 19 to 21 |
3.03 |
2.86 |
4.12 |
3.89 |
0.13 |
0.001 |
0.232 |
0.742 |
Keywords: Feed restriction, Milk composition, Dairy cows