March 1966

FACTS #31

THE RELATIONSHIP OF MILKING MACHINES TO MASTITIS*

Larry E. Stewart, Extension Agricultural Engineer**

What is the relationship of milking machines to mastitis? This question is of vital importance and should be uppermost in the mind of every man who operates a dairy farm or milks cows for a living. Unfortunately, the answer cannot be so directly stated as the question. In general, the direct and correct reply to the question would be ­ milking machines do not cause mastitis, IF:

1. The milking equipment selected for a particular farm operation is that which is best suited for the management, labor, and physical facilities available.

2. The system is properly installed according to manufacturer's recommendations with the primary concern being that of an efficient milking operation that does not put unnecessary stress on the cows.

3. The system is properly functioning at a constant recommended vacuum level.

4. The complete milking system is regularly maintained, periodically tested, and deficiencies corrected.

5. the equipment is properly utilized by the operator doing the milking.

Admittedly these are big IFS. Any milking operation which causes discomfort to the cow and which is caused by faulty equipment or improper techniques may lead to injury or mastitis. Many combinations of improper installation, operation, and utilization of milking equipment may create situations which will irritate or bruise the teat or udder tissues. The purpose of this discussion is to describe the operating conditions that create such problems and how these problems can be avoided.

Problem 1. Machine on Cow ­ No Milk in System

If a milking machine is operating at normal vacuum of 13 to 15 inches of mercury and sufficient air is moving, it is not likely to irritate the cows teat and udder ­ unless it is on the cow when there is little or no milk in the teat and udder cisterns. Milk acts as a lubricant. In its absence the machine may cause the membranes to rub together and, of course, produce irritation.

This condition exists when:

1. The machine is placed on the cow without proper stimulation or before the stimulation has resulted in let down of milk. It is essential that the udder be massaged for 1/2 minute with a towel dipped in warm (110-120^oF) antiseptic solution to start the let down of milk. Then 3 to 4 streams of milk should be removed from each teat by hand stripping into a strip cup. The teat cups should be attached within 1 minute following stimulation, or as soon as the teats are full of milk.

2. The milker is left on after the cow is milked out. Overmilking is probably the most common cause of udder irritation. Most cows can be milked out in 3-1/2 to 4 minutes yet many milking machine operators make a habit of leaving the unit on the cow 2 to 4 times this long. When milking machines are left on too long, the operator is usually attempting to handle more than the recommended two units per man.

Problem 2. Inadequate Air Flow ­ Vacuum Fluctuations

Inadequate air flow capacity, inadequate vacuum level, and excessive vacuum fluctuations are common complaints against mechanical milking systems. In pipeline milkers the milking vacuum frequently varies with every pulsation. This fluctuation should not be more than 1 inch of mercury during normal operation and the operating vacuum level should be restored within 3 seconds. If the low vacuum level occurs during the rest phase, there may not be sufficient pressure differential between the inside and the outside of the liner to cause its complete collapse and irritation results.

If the milking vacuum varies so that its low point is during the milking phase, it may case "ballooning" of the liner and teat. Ballooning occurs because the vacuum inside is less than the vacuum outside of the liner, causing it to expand. With vacuum applied to the teat, it tends to expand with the liner. This stretching of the teat membranes again is a source of irritation. The same type of irritation may be caused by liners that are too large for the teats, as is frequently the case with large bore liners.

What causes these vacuum fluctuations at the teat cup? There are many causes but the more common ones include:

1. Inadequate vacuum pump capacity. The size needed for a particular dairy operation depends upon a number of factors. Among these are:

a. number of milking units
b. size and length of pulsated lines
c. type of pulsator
d. type of system (i.e., bucket or pipeline)
e. requirements of other vacuum operated equipment

The vacuum pump is rated by the amount of air that it is capable of moving, measured in cubic feet per minute (CFM) at a specific vacuum level (inches of mercury). The pump selected should be capable of moving 3-4 CFM per milking unit for the bucket system and 5 CFM per unit for a pipeline system. Follow the manufacturer's recommendations on other system components to be sure that the pump possesses adequate CFM capacity at the operational vacuum level.

2. Restricted or undersized vacuum lines. Very few dairy farms can boast of having more than adequate vacuum lines. Typically cow numbers are increased without having the system redesigned. Added milking units, small vacuum lines, too many bends, or too many fittings greatly reduce the amount of air that a vacuum pump can remove. Often vacuum lines are partially clogged by milk solids, dust, dirt, cow hair, and other debris. Obviously anything other than a clear line of proper size restricts free movement of air for adequate vacuum.

The minimum recommended diameter for vacuum lines for any milking system is 1-1/4 inches. The reason for this recommendation is easier to understand when the relationship of friction loss to pipe diameter is considered. As compared to 1-1/2 inch galvanized pipe for an equal volume of air flow:

1-1/4 inch pipe has 2-1/2 times more friction loss
1 inch pipe has 7 times more friction loss
3/4 inch pipe has 20 times more friction loss

The effect of elbows and tees should also be considered. Tees and 90^o elbows for 3/4 inch pipe have a friction loss equal to 2.1 ft of 3/4 inch pipe, for 1 inch pipe the equivalent of 2.6 ft of pipe; for 1-1/4 inch pipe the equivalent of 3.5 ft of pipe, and for 1-1/2 inch pipe the equivalent of 4.1 ft of pipe. The system should be planned to avoid an excessive number of pipe fittings.

3. Vacuum controllers undersized or sticking. The vacuum controller (regulator, relief valve) is the vacuum limiting valve that prevents the vacuum level from exceeding a set value by admitting atmospheric air as necessary. During normal operation, the vacuum controller should admit air into the system at all times except when the vacuum level drops below operating level. The controller should then close rapidly and remain closed until the normal level is restored. For safe operation, the controller should be placed between the first stall cock and the vacuum pump. When no milking units are operating, the full pump capacity of air should be passing through the control valve.

It is very poor practice to try to compensate for abnormal vacuum levels by adjusting the controller. Once the controller is adjusted for the proper vacuum level, it should not be changed. In most cases, some factor other than controller malfunction will cause variations in the vacuum level. It is very important that the controller be periodically checked. The manufacturer's recommendations for maintenance and service should be consulted and followed.

4. Milk from unit entering bottom half of milk pipe. The milk inlet valves should be installed so that milk and air from the milking unit enter the top half of the milk pipe. This method makes it possible to maintain a vacuum column between the pipeline and teat cup and also reduces the possibility of spreading mastitis organisms due to back flushing of infected milk.

5. Flooded pipelines. A maximum of 5 milking units per single 1-1/2 inch milk line is suggested in order to avoid flooding. When 5 or more units are planned, the milk line should be looped together and a dual-entry receiver used. The system can then accommodate up to 10 units. The use of larger diameter milk lines should be considered for systems of more than 8 milking units.

6. Vacuum reserve tank too small. Most vacuum systems installed today include a reserve tank. It has two purposes. First, it acts as a cushion to absorb any sudden inrush of air, which would otherwise result in a large vacuum drop. Second, it acts as a trap for liquid both while the system is operating and while it is being cleaned, thus protecting the pump from internal damage.

It is not easy to specify the size of tank needed for a given system. Sometimes the reserve tank comes with the pump. It should be large enough so that when the last of the total number of milking units being used is attached to the cow, the vacuum does not drop by more than one inch of mercury. A volume capacity of 5 gallons per milking unit may serve as a useful guide.

Adding a larger vacuum tank to an existing system is not always advisable. The larger tank size may compensate for sharp drops in vacuum level, but the recovery time may become excessively long if the vacuum pump is small. Thus, a small pump cannot be made to do the work of a large one by the addition of more or larger reserve tanks.

There are other factors that contribute to vacuum fluctuations but those previously discussed are the major items to consider.

Problem 3. Dirty or Worn Pulsators

The pulsator is the mechanical device to open or close ports permitting air to be pumped out from or to re-enter the space between the teat cup shell and liner. If the pulsator ports are dirty or worn the flow of air may be restricted so that the vacuum level is not reduced to zero; thus, the liner does not collapse completely. Therefore, the liner does not massage the teat of sufficiently reduce the vacuum applied to the orifice. Congestion of blood vessels and tissue fluids result. Also, it may be manipulating the teat with little or no milk in the cistern and this cause membranes to be rubbed together and produces irritation.

Problem 4. Confusion About Milk-Rest Ratios and Pulsation Rates

The milk-rest is the amount of time the pulsator draws vacuum to open the liner and withdraw milk, compared with the amount of time it admits atmospheric air to collapse the liner and massage the teat. It is expressed in percentage; typical recommended milk-rest ratios that can be used with complete safety range from 50/50 to 60/40. Ratios as wide as 75/25 are available from some equipment manufacturers. These units milk very rapidly but require careful supervision to avoid teat congestion. Such wide ratios also are more likely to cause irritation if malfunctioning occurs.

The rate of pulsation does not directly affect speed of milking; however, excessive rates may have adverse effects. Most modern milking machines perform ideally at rates of 48 to 55 pulses per minute if the remainder of the system is operating properly. Faster rates may not provide adequate teat massage or rest under varying vacuum levels. Such rates tend to deplete the vacuum reserve, since each pulsation admits a definite volume of air into the system.

Problem 5. Selection and Care of Shells and Liners (Inflations)

Liners can be classified as molded or stretch type and should further be specified as wide bore (greater than 3/4 inch inside diameter) or narrow bore. Generally, narrow bore liners with proper shells milk faster than large bore shells and liners. Narrow bore liners open faster since there is less volume between the liner and shell from which air must be evacuated. New stretch liners milk faster because they have greater resistance to collapse and thus are open for a longer interval in each pulsation cycle than most molded liners. However, as the stretch liner loses its elasticity with use, it has less resistance to collapse and is collapsed for a longer interval in the pulsation cycle, which results in slower milking. Excessively used liners coupled with low or fluctuating vacuum results in incomplete collapse of the liner and inadequate massage of the teat end. It is recommended that the dairyman have two sets of liners for each milking unit and alternate their usage on a weekly basis. The "extra" set should be soaked in a cold water-lye solution. It is reported that two sets, when used alternately, may have the equivalent life of three sets used continually.

Summary

Normal milking machine operation, coupled with a conscientious operator will harvest the milk crop at maximum efficiency with no discomfort or injury to the cow. Improper installation, operation, or milking technique may create stress on the cow that can lead to mastitis. Each dairyman should be familiar with the mechanical milking system, how it works, symptoms of poor operation, and what effect improper operation may have on his cows. This knowledge, along with a program of periodic testing and correction of deficiencies of the entire milking system by a qualified milking equipment serviceman, can do much to reduce mastitis losses due to lost milk production, lost milk and the cost of drugs and veterinarian fees.

*For basic information on "How Milking Machines Work," Extension Bulletin No. 211 will be released about May 1966.

**Acknowledgement is given to Dr. James L. Cason, Department of Dairy Science for his suggestions on the preparation of this text.

 Facts #31