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Composition, chemical analysis, and nutritive value of diets fed to cows during lactation

 
Item 30–60 d, % of DM 120–150 d, % of DM 240–270 d, % of DM
Ingredient
    Corn silage 26.49 26.71 28.98
    Alfalfa hay 9.75 10.38 11.18
    Grass hay 8.14 10.02 9.92
    Commercial concentrate mix1 55.62 52.89 49.91
Nutrients and DMI
    DMI, kg/d 23.98 24.74 22.93
    Crude protein, % DM 15.28 15.05 14.38
    Starch, % DM 26.04 24.81 25.23
    NDF, % DM 34.12 35.31 34.35
    NDF from forage, % DM 20.70 22.46 22.89
1Composition on as-fed basis: 41% corn flour, 17% dried beet pulp, 13.4% soybean meal, 10% wheat bran, 5% sunflower meal, 4% sugar beet stillage, 3.1% Ca-soap of palm fatty acids, 2.2% potato protein flour, 1.3% limestone, 1.2% sodium bicarbonate, 0.9% dicalcium phosphate, 0.6% magnesium oxide, 0.3% sodium chloride.



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Descriptive statistics of main milk components and GGT activity

 
Item1 Mean SD Minimum Maximum Median
Fat, % wt/vol 3.95 0.54 1.94 5.43 3.91
Protein, % wt/vol 3.29 0.32 2.46 4.35 3.27
Lactose, % wt/vol 5.11 0.17 4.03 5.52 5.10
SCC, log (n/mL) 4.65 0.39 3.84 5.59 4.69
GGT, U/L 3,453 707 1,515 5,574 3,464
1GGT, γ-glutamyl transferase. Activity measured on defatted milk; SCC, somatic cell count.



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Milk yield and milk characteristics in cows categorized according to the average GGT activity of milk during lactation1

 
P-value3
Item High Low SEM2 Gr Gr × DIM
Milk yield, kg/d 40.81 42.76 1.7185 ns <0.001
Fat, % w/v 4.04 3.86 0.1247 ns ns
Protein, % w/v 3.39 3.18 0.0741 0.014 <0.001
Lactose, % w/v 5.11 5.09 0.0500 ns <0.001
Titratable acidity, °SH/50 mL 3.75 3.45 0.0852 0.022 0.0548
SCC, log(n/mL) 4.71 4.59 0.0870 ns ns
Rennet coagulation time, min 17.40 17.72 1.1659 ns ns
Curd firming rate, min 6.37 6.99 0.9408 ns 0.0016
Curd firmness, mm 28.56 25.24 2.7404 ns ns
GGT4, U/L 3,862.67 3024.02 100.5900 <0.001 ns
1High, cows with greater average GGT activity in milk during lactation (n = 10); low, cows with lower average GGT activity in milk during lactation (n = 10); GGT, γ-glutamyl transferase; SCC, somatic cells count.
2Greatest SEM.
3P-values: Gr is the group effect (high vs. low); ns, not significant; days in milk (DIM) was always significant.
4Measured on defatted milk.



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Multiple regressions by using GGT activity of milk (U/L) as the dependent variable and milk yield and its fat and protein content as independent variables1

 
Item 40–70 DIM2 140–170 DIM 250–280 DIM
Regression
    n 66 64 53
    R2 0.47 0.24 0.16
    P-value <0.001 <0.001 0.013
    Independent variables
        Milk yield, kg/d
            Coefficient −15.32 −27.99 −41.06
            SE 9.29 13.15 15.22
            P-value 0.104 0.037 0.001
        Milk fat, %
            Coefficient 340.86 41.02 57.93
            SE 121.83 194.44 171.59
            P-value 0.0069 ns3 ns
        Milk protein, %
            Coefficient 1,523.65 613.59 394.90
            SE 316.34 287.87 543.65
            P-value <0.001 0.037 ns
1GGT, γ-glutamyl transferase. Activity measured on defatted milk.
2DIM, days in milk.
3ns, Not significant.



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Metabolic profile of cows categorized according to the average GGT activity of milk during lactation1

 
P2
Item High Low SEM Gr Gr × DIM
PCV, L/L 0.28 0.29 0.0106 ns <0.0001
Glucose, mmol/L 4.16 4.03 0.0801 ns <0.0001
Total cholesterol, mmol/L 7.29 6.66 0.3922 ns <0.0001
Urea, mmol/L 4.66 5.23 0.3696 ns <0.0001
Ca, mmol/L 2.56 2.51 0.0486 ns ns
Inorganic P mmol/L 1.90 1.86 0.0856 ns 0.0008
Mg, mmol/L 1.09 1.12 0.0136 ns 0.0006
Na, mmol/L 143.20 143.26 0.5408 ns <0.0001
K, mmol/L 4.07 4.01 0.0498 ns ns
Cl, mmol/L 104.61 105.73 0.4889 ns 0.0108
Zn, μmol/L 13.65 12.25 0.6026 ns ns
Ceruloplasmin μmol/L 2.28 2.56 0.1798 ns <0.0001
Total protein, g/L 81.87 81.07 1.3223 ns <0.0001
Albumin, g/L 38.11 37.42 0.7672 ns <0.0001
Globulin, g/L 43.9 43.75 1.6162 ns 0.0013
Haptoglobin, g/L 0.12 0.09 0.0254 ns <0.0001
AST, U/L 83.10 104.58 5.3491 0.0169 <0.0001
GGT, U/L 3.46 3.46 2.6317 ns <0.0001
AP, U/L 31.38 31.52 3.5841 ns 0.0208
Total bilirubin, μmol/L 1.05 1.12 0.1229 ns <0.0001
1High, cows with greater average γ-glutamyl transferase (GGT) activity in milk during lactation (n = 10); Low, cows with lower average GGT activity in milk during lactation (n = 10). Activity measured on defatted milk. PCV, packed cell volume; AST, aspartate aminotransferase; AP, alkaline phosphatase.
2P values: Gr is the group effect (high vs. low); ns, not significant; days in milk (DIM) was always significant.