WEIGHING AND SAMPLING MILK FOR DHI TESTS

DAIRY HERD IMPROVEMENT
1985

OLSON, C.C., & AMICK, D.D.
VOLUME: NCDHIP HANDBOOK

Correct Procedures Are Important

The only way we can know how much milk, butterfat or protein a cow
actually produces is to weigh and test a sample from every milking,
every day throughout her lactation. Dairy producers and others
using Dairy Herd Improvement (DHI) records realize this would be
very impractical because of cost and inconvenience. Instead,
methods of weighing, sampling, testing and computing production
credits have been developed by which an accurate estimate of a
cow's actual yield based on 1-day tests taken at monthly intervals
can be made.

These methods are spelled out in the DHI rules. Accurate records
can be obtained only when rules are followed, equipment used meets
requirements and when dairy producers, supervisors and technicians
do their work properly.

The importance of following correct rules and procedures can be
illustrated with a cow that has a 305-day record of 20,000 pounds
of milk and 800 pounds of butterfat. During this lactation:

- the cow will be tested 10 times or 3.3 percent of her days in
milk,

- with bucket milkers, the dairy producer will lift 655 pounds on
test days,

- with a pipeline, only 14 pounds of milk will be observed in the
meter,

- the supervisor will obtain only 1-1/3 pounds in the samples and

- the lab equipment will use only 1/4 of an ounce during the 10
tests and must accurately represent the 20,000 pounds of milk
produced.

Obviously, the accuracy of DHI records depends on trained personnel
and proper use of approved equipment. The information also suggests
why additional verification tests are needed for cows and herds
with unusually high records.

Sampling in Herds Without a Pipeline

Problems and errors are most likely to occur when milk yield is not
normal or when samples are taken or handled improperly on test day.
Here are the major items a dairy producer should consider to ensure
that monthly samples represent the average daily production of milk
and butterfat for the test period and a cow's normal milk yield for
a 24-hour period on test day.

1. Milk at the regular time. (To make 24 hours in the test period,
the AM milking should begin at the same hour when the AM milking
began the day before.)

2. Stimulate the cows to let down their milk no more than 1 minute
before attaching the milking machine. (Delays can cause low
butterfat tests.)

3. Milk rapidly and do not overstrip on test day.

4. Do not handstrip unless also done on other days.

5. Milk cows in the same order as on other days.

What Must Be Reported for Each Test?

A preprinted barnsheet is provided for reporting the following
information for each test day. This barnsheet is mailed or
delivered with the sample bottles. Use it in the barn to help
reduce errors and ensure that all data have been provided to enable
processing by the computer without delay.

a. The pounds of milk produced by each cow at each milking on test
day.

b. The number of the sample jar containing the milk taken from each
cow that has milk weights.

c. Codes to indicate any condition or problem affecting reliability
of milk samples or weights taken on test day.

d. Dates when cows died or were fresh, dry or sold, all of which
indicate the beginning or ending of lactation. A barn calendar
record of these events will ensure complete and accurate transfer
of these important records to the barnsheet.

e. The name and identification of new cows added since last test.

f. Some states also require feed inputs, quality codes, prices of
feed fed and milk sold.

g. Breeding records, service sires and calf identification records
should be reported to provide the means for genetic improvement.

Set the Scale

Set the scale on zero to exclude the weight of the pail. Record
milk weights to the nearest 1/10 pound on the barnsheet ---
recopying can cause errors.

A method especially useful in a large parlor herd on AM-PM test is
writing the cow's name and milk weight on the cap of each sample
bottle during milking and then transferring that information to the
barnsheet after milking is completed.

Identify the Sample Bottles

For accurate and correctly reported sampling from the testing
laboratory, each cow and her corresponding sample number must be
identified. At the completion of each test, check the sample
bottles to ensure that milk is present for all cows with milk
weights and check that the sample bottles of dry cows that have
left the herd are empty.

Mix Before Sampling

The first milk obtained from the cow is extremely low in butterfat
and the last is extremely high. Therefore, to obtain a
representative butterfat test, collect all of the cow's milk,
including strippings. Mix milk well before taking the sample.

To mix, pour milk from the milker bucket into the weigh pail. If
there is any delay between mixing and sampling or if cows are
handstripped after machine milking, pour the milk a second time.

Sampling Procedure

If you mix the milk well, it makes no difference whether the sample
comes from the top, middle or bottom of the pail. Take a full
dipper in the first milking and a proportionate sample from the
second.

Protect Sample Quality

Dichromate pills (or powder) or other approved preservatives are
added to each bottle to preserve the milk samples. Preservatives
will dissolve in a few seconds after milk is added. Make sure you
mix the milk and preservative well by rotating the bottles as they
are filled or by gently rotating the whole box after you complete
milking. Mix each bottle again as you take the morning sample.

Thorough mixing with the preservative is especially important in
summer months. Do not allow samples to freeze in winter or get too
warm in summer.

Weighing and Sampling Milk for the Dairy Herd Improvement
Association (DHIA) in a Pipeline Milking System

Weighing devices used in herds enrolled on official DHI test must
have been approved by the National Dairy Herd Improvement Policy
Board and must be owned by the local DHIA.

You need one meter with appropriate hoses for each milker unit.
Rental cost on test day varies with either the number of meters or
the number of cows in the herd, and who takes the samples. In herds
on official test, a DHIA supervisor must weigh and sample, but this
sampling service also is available for herds on unofficial test.

How to Obtain a Representative Milk Sample

During milking, a fixed portion of each cow's milk flowing through
the meter is diverted into a collecting tube (Tru-Test or Waikato)
or into a sample cup (Milk-0-Meter or Boumatic).

The milk must be thoroughly mixed before sampling because the
butterfat content of milk varies during milking.

Data in Table 1 clearly emphasize that butterfat tests will be
incorrect unless milk is mixed and a representative sample is
taken. The kind of meter used influences the direction of error
(high or low).

With a Tru-Test meter (tester model) milk will be adequately mixed
only by pouring milk from the collecting tube into another
container or by placing a cap on the tube and inverting it at least
twice. (Milk will not be sufficiently mixed by shaking the tube
from side-to-side.) After mixing, milk needed for the sample is
poured into the sample bottle.

In Tru-Test (farmer model), Milk-O-Meter, Waikato or Boumatic
meters, milk is mixed by opening the sampling valve while vacuum is
still on the meter. After air has bubbled through the milk for 3 to
5 seconds, the vacuum is turned off and milk drops into the sample
jar. An alternate method of mixing is to turn off the vacuum, empty
all milk into another container, and then pour the required amount
of milk into the sample jar.

TABLE 1. Content of milk taken at 1-minute intervals*

Pounds
Milking of milk Solids-
Period obtained Butterfat Protein not fat
Percentage --
1st minute 5.1 2.3 3.2 8.7
2nd minute 6.7 3.2 3.2 8.9
3rd minute 7.2 4.3 3.2 8.8
4th minute 10.4 5.4 3.1 8.7

Average test for 29.4 pounds = 4.10% 3.16% 8.76%
* Pennsylvania DHIA data.

How to Make Meters Work

a. Have enough vacuum. The pump should have enough capacity to
handle one more milker unit than is used at milking time. This
extra pump capacity is needed to handle meters and is a factor that
should be considered when planning a new pipeline installation.

b. Keep air bleed clean. Tube-type meters bring milk up through a
vertical tube to a spreader cone at the top. As milk falls, a
proportion of the milk falls through the diverter into the
collecting tube. This "coning action" depends on air injection at
the milker claw and will not happen unless the air bleed is kept
open and free of debris. Tube meters cannot be used on a Zero
pipeline system because the meter does not cone properly, unless
properly fitted with a special attachment that allows air to enter.

c. Avoid air leaks. The proper amount of milk does not fall into
the collecting tube or sample cup unless gaskets seal properly. Air
leaks around the sampling valve can cause the same problem. Air
leaks also are serious if the milk pump is operating at near
capacity. Excessively long hoses will adversely affect vacuum
levels.

d. Read accurately. Volumetric calibrations on the side of the
collecting tube are used to read milk yield. Ignore the foam line
and read the milk line. Use a pen flashlight if necessary.

e. Avoid vibration and make sure meter brackets are level. These
factors are most important with Milk-0-Meters. Keep other meters
reasonably level.

Using Weigh Jars for Milking Parlors

Weigh jars work well in a milking parlor. They should be considered
during construction, leaving enough room for installation of a
sampling device between weigh jars and milk lines. They should be
rigidly mounted at each milking stall. Manufacturers indicate on
the label whether weigh jars are approved for use in DHI herds.

Weigh jars are similar to a milker bucket since both retain all
milk for final weighing and sampling. Read the milk weight from the
scale or from the volumetric reading on the side of the jar.

Wait 30 seconds for the foam to dissipate before you read the milk
line on jars. Occasionally determine if readings are identical on
both sides of the jar. If readings are the same, the weigh jar was
installed correctly and is mounted in a vertical position to permit
accurate weights.

Milk should be mixed properly before taking the sample. The vacuum
is left on and the sampler valve opened to allow air to enter and
mix the milk. Allow air entry for as long as 1 second per 2 pounds
of milk in the jar. Proper mixing is especially important if the
weigh jar is nearly full of milk.

Turn off the vacuum to the jar after mixing and use the sample
bottle to collect about 1 ounce of milk from each milking. (Collect
2 ounces of milk if the herd is on AM-PM test.)

Electronic Meters

The most recent developments in metering milk yield involve
electronic meters developed and sold by milking machine companies.
They take up less space in the parlor, are easier to clean and have
the advantage of a direct electronic readout, which in some
installations can be retained in the system or on tape.

Although the dealer has responsibility for proper installation and
maintenance, the supervisor must learn the principal features of
its operation and be diligent in observing that the unit is working
property during the milking process to ensure correct weights and
samples.

The sampling process itself is not markedly different from the
meters. Minimum requirements for mixing before sampling must be
carefully observed. Frequent checks, comparing total milk yield
represented on the barnsheet with bulk tank weight, are
recommended.

All people involved in the DHI program must make a continuous
effort to ensure accuracy in estimating a cow's production. Proper
maintenance and handling of the equipment at the farm and in the
lab, as well as proper technique in collecting, handling and
analyzing milk samples, are necessary for accurate estimates.

תתתתתתתתתתתתתתתתתתתתThe National Dairy Database (1992)תתתתתתתתתתתתתתתתתתתת
תתתתתתתתתתתתתתתתתתתתתתת\NDB\DAIRY\TEXT\DA109100.TXTתתתתתתתתתתתתתתתתתתתתתתת

%f TITLE;WEIGHING AND SAMPLING MILK FOR DHI TESTS
%f COLLECTION;DAIRY HERD IMPROVEMENT
%f ORIGIN;Wisconsin
%f DATE_INCLUDED;June 1992