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.
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
2. Insert 12-gauge needle into top of milking claw through short
milk tube -always clean needle after insertion into rubber
3. Attach the Digimet to 12-gauge needle with Digimet in vacuum
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