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Component Variation During the Milking Process

By Bill VerBoort, General Manager, California DHIA

 

The components in milk are known to vary based on several factors. Factors such as stage of lactation, milking practices, weather conditions, and the breed and genetics of the dairy cow can affect the components of the milk produced. Proper sampling technique can also affect the component results.

Methodology
As part of the determination of why some cows have either extremely high or low component tests, the California DHIA undertook a study to investigate the implications for variation based on the stage of the milk letdown process. To do so, 40 cows at the Fresno State University dairy were sampled. Prior to sampling, last test day milk production and most recent daily milk (based on the dairy's electronic Boumatic milk meters) were examined. Based on the previous milk, samples were taken from the milk produced at each quartile of milk production (4 quartiles divided into approximately 25 percent each). Since the total amount of production was not known until the cow finished milking, all data obtained was not necessarily useable. Data was only used if the production fell into the following categories:
  1st quartile 20% - 30% of total production
  2nd quartile 45% - 55% of total production
  3rd quartile 70% - 80% of total production
  4th quartile 100 % of total production
Results were also not used if there were missing component results because of insufficient sample volume or other reasons. In the final analysis, data from eighteen cows were in appropriate milk volume range as well as having components for butterfat, protein, lactose, solids-not-fat, and somatic cell count. Twelve of the cows were Holstein and six of the cows were Jersey.

Results
The component results were analyzed based on all the cows in the study, by breed, by days in milk (less than or greater than 150 days in milk), and by lactation number (1st, 2nd, and 3rd or greater). The results of the study appear on the following page.
In all categories, the butterfat was lowest in the first quartile of the letdown process and continued to increase as the milking progressed. The level of increase was approximately 3 times greater in the last quartile than the first. 
Protein levels were quite constant, peaking slightly in the second and third quartile. Lactose was also fairly constant. The lactose component started at a level and decreased only slightly as the milking process continued. The pattern for solids-not-fat was similar to lactose. The pattern for somatic cell analysis started low in the first quartile, increased slightly in the second, dipped again in the third quartile, and was highest in all cases in the last part of the letdown process.

Implications for DHIA
Proper sampling is imperative for accurate records. Based on the research conducted, sampling at various stages of the letdown process can have a major effect on the butterfat content of the sample. There is less effect on the other components. However, somatic cell counts do show considerable variation over the milking process. 
Taking samples that represent only a part of the milking process (either the first or the last part of the milking process) will yield results that are not indicative of the overall milk production. Based on the type of meter used, inaccurate sampling can occur. This may occur because of malfunctioning samplers, inadequate agitation, or inappropriate proportional sampling. The differences are most pronounced with the butterfat and somatic cell component of the milk but also occurs at lower levels with protein, lactose, and solids-not-fat. Obtaining a representative sample from the complete letdown process is the only acceptable method of sampling milk for accurate component analysis.

 
All Cows 
All Cows - 18 cows 

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

1.91

3.49

4.77

9.24

169

2

3.24

3.54

4.79

9.23

233

3

4.47

3.53

4.69

9.08

177

4

5.97

3.49

4.54

8.81

321

By Breed 
Holsteins - 12 cows

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

1.81

3.25

4.75

8.93

208

2

2.77

3.29

4.78

8.95

300

3

3.97

3.29

4.68

8.80

228

4

5.24

3.25

4.53

8.55

425

Jersey - 6 cows

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

2.10

3.98

4.82

9.85

89

2

4.20

4.03

4.82

9.80

99

3

5.47

4.02

4.73

9.65

76

4

7.42

3.97

4.57

9.33

113

By Days in Milk 
Less than 150 days in milk - 8 cows (5 - H/3 - J)

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

1.73

3.40

4.88

9.24

133

2

3.25

3.41

4.83

9.14

186

3

4.33

3.40

4.75

9.00

148

4

6.05

3.39

4.61

8.76

153

More than 150 days in milk - 10 cows (7 - H/3 - J)

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

2.05

3.57

4.69

9.24

197

2

3.24

3.64

4.76

9.31

270

3

4.58

3.64

4.65

9.15

201

4

5.90

3.57

4.48

8.85

455

By Lactation 
1st lactation - 5 cows (4 - H/1 - J)

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

2.14

3.40

4.70

9.10

124

2

2.90

3.48

4.82

9.20

49

3

4.16

3.48

4.70

9.02

84

4

6.04

3.42

4.56

8.78

173

2nd lactation - 7 cows (5 - H/2 - J) 

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

1.94

3.49

4.86

9.29

171

2

3.00

3.53

4.83

9.27

315

3

4.31

3.51

4.73

9.11

225

4

5.81

3.47

4.57

8.81

378

3rd lactation and above - 6 cows (3 - H/3 - J)

Quartile

% Fat

% Pro

% Lactose

% Snf

Av SCC

1

1.67

3.58

4.73

9.30

203

2

3.82

3.60

4.72

9.22

290

3

4.90

3.60

4.65

9.10

200

4

6.08

3.57

4.48

8.83

377

 


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