|
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 |
|
