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Doc's Corner Article 110-B

Digimet Accessories

Cluster Decay Test

The Cluster Decay Test was developed to determine to what level the vacuum has decayed (reduced) to before milking unit is removed from cow's teats. Experience has shown that milking unit removal under vacuum load can contribute to bacterial invasion of the mammary gland with the potential of mastitis.

No data is available to my knowledge that states at what vacuum level is safe for milking unit removal - present thinking is that this level must be below 1.5" Hg.

Equipment required:

1. Digimet
2. 3 inch - 12 gauge needle
3. Needle cleaner (0.041" diameter)
4. Silicone sealant

This testing procedure utilizes the five graph storage areas within the Digimet. The test is repeated five times on five different milking cows at the time of milking unit removal.


1. Performed at end of milking, with automatic removal in manual mode.
2. Insert 12-gauge needle into top of milking claw through short milk tube -always clean needle after insertion into rubber tubing.
3. Attach the Digimet to 12-gauge needle with Digimet in vacuum graphing mode.
4. Keep the Digimet elevated above point of needle insertion to avoid milk in hose between needle and Digimet.
5. Make certain Digimet is in the 10-second recording mode.
6. When all is ready - Press the Enter key to begin recording and when the R starts to blink in the upper right corner of the Digimet display window, press button on automatic removal for manual removal of milking unit.
7. Remove needle when blinking stops
8. Repeat on four more cows
9. When 12-gauge needle removed - close hole with sealant

-This information should be downloaded to computer for permanent records of vacuum decay at time of milking unit removal.
-If indications of unit removal in less than 500 milliseconds corrective action must be taken.


-- When milking unit is removed under load, the graph will show an abrupt drop from some elevated vacuum level to atmospheric pressure in less than 250 milliseconds.
-- Present understanding is that any rapid drop in vacuum from above 1.5” Hg in less than 250 msec. could create a pressure change at teat end which could project bacteria into the mammary gland creating a potential for mastitis.
--To correct the problem, one must make certain vacuum drops below 1.5” Hg before unit removal. Options are: 1. Increase size of cluster vent to maximum of 0.041” diameter. 2. Utilize vented liners leaving claw vent open. 3. Delay retraction time, but obviously unit must be retracted prior to falling on the floor. 4. For certain vacuum must be below 1.5” Hg prior to removal.

Developed by: Western Dairies, Inc.
Research and Development - Lionel H. Brazil DVM

Doc's Corner is a contribution of Lionel H. Brazil, DVM (1928-2007). Dr. Brazil offered dairy consultation services worldwide for many years. His services covered the following areas: milking management, vacuum system evaluation; and all management procedures relating to mastitis control and SCC reduction.


 Copyright© 2010 L. J. Engineering, Inc. All rights reserved. Revised: June 8, 2010