Doc's Corner

Doc's Corner Bulletin 112

March 30, 2006

“The missing link in mastitis control” or

What’s new in Mastitis Control

Most who are involved in mastitis control are very aware of the cardinal areas in which they attempt to correct when solving a mastitis problem.
In order of importance, one can specify:

 - cows must be clean and dry prior to milking unit application
 - sprinkler pens must be working properly
 - high level of sanitation in milking parlor
 - clean floors and clusters
 - clean milkers hands
 - sanitizer in drop hoses
 - proper procedures must be followed
 - pre-dipping
 - fore-stripping
 - wiping clean after 30-60 seconds
 - milking unit application within 30-60 seconds after teat manipulation
 - post-dipping
 - adequate vacuum stability
 - proper vacuum level
 - proper pulsation rate and ratio
 - high degree of repeatability
 - minimal variability
 - environment
 - well maintained open corrals
 - properly groomed free-stalls
 - bacterial identification
 - correct treatment

Unfortunately, in many cases, when all the items listed above are corrected, the elevated SCC and mastitis levels remain to be a problem.

It is my opinion that a major problem causing mastitis is the fact that in many situations, the milking unit is removed from the mammary gland under load conditions - meaning that the milking vacuum level within the milking cluster has not had time to return to atmospheric pressure before the retract cylinder jerks the milking unit from the individual teats.

It is a well-known fact that abrupt removal of the cluster from the teats is very harmful to teat end tissue and can contribute to increased levels of mastitis.

Adequate vacuum decay time is the time it takes the milking vacuum in the milking cluster and milk hose on the cow side of the close-off valve (attached to the milk hose) to decay (or to approach atmospheric pressure) to safe levels prior to the retraction of the cluster by the retract cylinder. There is insufficient research available that tells one the safe level for removal of the milking cluster. For now, it is my opinion that vacuum must decay to at least 1.5" Hg, within the cluster, prior to removal of the milking unit. In many cases, as soon as vacuum is closed to the cluster, the milking unit begins to fall from the teats, but this is too variable to depend upon at all times.

In present automatic milking equipment, the only mechanism for this residual vacuum to dissipate is through the vent hole in the milking claw. With this knowledge, it is apparent as to why this vent must be clear of debris at all times. Under current ASME standards this vent should leak approximately 0.5 CFM, which relates to a 0.040 diameter hole. Unfortunately one can find these very important vents to be of various sizes from different manufactures on present day dairies.

The mechanism for this removal is slightly complicated and very often neglected. The removal process begins with either an electric sensor or milk meter telling the automatic removal system when it is time to remove the claw from the teats. When this time arrives, based on milk flow, the sensor or meter signals the open/close valve installed within the milk line between the cow and stainless steel milk pipe line to close - shortly after closure, or often simultaneously, a signal goes to the retract cylinder to pull the cluster from the cows teats before the milking unit falls to the floor. Generally, if teats are small, the unit can fall to the floor within 2 to 4 seconds, so timing is important. With this in mind, it becomes apparent as to the importance of routine maintenance of equipment to assure that all of above occurs in a timely fashion and again, the extreme importance of the cluster vent hole.

In many cases the milk flow sensor and the close off valve are constructed as a single item while in some automatic milking systems the sensor and close off valve can be separate - especially if milk meters are involved.

The present method of determination of the occurrence of improper decay is to graph the vacuum level within the milking cluster just prior to activation of removal button for at least 10 seconds to determine the decay pattern after the milk valve closes. Normally one sees a gradual downward graph to some point near atmospheric pressure within a 2 to 4 second period. An abrupt downward movement in the graph to atmosphere in less than 250 milliseconds would be considered detrimental to teat end health and require correction. Under some conditions this inadequate delay of vacuum decay can be observed when one sees the udder pulled sideways by the claw just prior to a break in suction of the individual teat cups.

Not only can the plugged vent be incriminated, but very often the milk closure valve can leak, if faulty, after it receives the signal to close. This obviously would be a major concern and can cause extreme damage to teat end epithelium at the time of cluster retraction.

It becomes obvious that the cluster vent must be sized properly to 0.040" diameter and maintained in an open condition at all times. If this diameter of a hole allows insufficient air to enter claw, one can utilize vented liners to aid in correcting the problem. In no situation would I recommend closure of the cluster vent if vented liners were to be used. The additional air through the vented liners does not cause a vacuum drop of any significance. It seems that the 0.040" diameter vent has become standard over the years and to avoid possible future liability, it is best to leave at that size.

Several tests are available to assure proper functioning of equipment at time of milking unit removal.

1. Visual observation can be important, but often neglected as to significance
2. The Ping-Pong ball test
 --- Dis-engage the milk hose from the pipe line side of the sensor/milk closure valve
 --- Hold Ping-Pong ball to within a quarter of an inch to sensor/closure valve
 --- If there is any vacuum leak - the ball will snap to the sensor/closure valve
 --- Must be corrected immediately
3. Check retraction time of retraction cylinders with stopwatch
 --- Retraction time of all cylinders should be +/- one second
 --- Adjust if possible
4. Special ohmmeter to determine proper milk flow at time of removal or annual calibration of milk meters

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.