The two most common reasons for milking system problems on most dairy farms in the mid-1990's are: inadequate system capacity to cope with rapidly increasing levels of production per cow, and inadequate routine maintenance of milking equipment. Often, systematic visual observations can indicate the milking machine faults likely to be associated with mastitis or teat condition problems, or with slow or incomplete milking. The following ten simple checks are not intended to replace regular machine testing and servicing by qualified technicians. Instead, they are recommended as supplementary tests which can be carried out by anyone who is interested in preventive maintenance and good milking performance.

The tests or observations are grouped into three sections:

1) checks that should be made during milking;
2) checks made with the machine running but not milking; and
3) checks that can be made while the machine is not running.

No specialized testing equipment is required apart from a stop watch, spirit level, and a vacuum gauge of known accuracy.

The four best guides to machine function during milking are:

Short-term changes. Ideally, teats should be as soft and supple just after milking as before milking. Teats that are slightly swollen or hard (due to congestion or oedema), or slightly blue or purple in colour (cyanotic) after milking result from machine-induced, circulatory impairment. Usually, teats are thicker after milking with wide-bore liners, or at high vacuum level. Cyanosis or oedema around the teat apex or lower barrel often indicates some type of pulsation failure such as insufficient collapse phase of pulsation, short teatcup liners or liners with insufficient tension. Cyanosis or oedema around the upper barrel of the teat may be due to liners with hard mouthpiece lips or high mouthpiece vacuum.

Longer-term changes. Healthy teat skin provides the best defence against all types of pathogens. Furthermore, smooth healthy teat skin is easier to clean and easier to keep clean compared with rough or damaged teat surfaces. The act of milking aggravates all types of teat lesions. Machine milking is the main cause of hyperkeratosis (teat canal erosion, or orifice erosion), petechial haemorrhages (haemorrhagic blisters) near the teat end, and may exacerbate teat chapping.

A high incidence of teat orifice abnormalities, such as hyperkeratosis or radial cracking, ("rings" or callouses) may result from excessive vacuum , over-milking, hard liners or liners mounted at un-necessarily high tension. Petechial haemorrhages around the teat end, and possibly "black spot" at the external teat orifice, are reasonable indicators of some type of pulsation failure such as short teatcup liners or insufficient collapse phase of pulsation.

Factors other than machine effects also cause or aggravate teat lesions, of course. Teat lesions occur in beef herds and hand-milked cows too! Teat lesions associated with a herpes virus (possibly similar to the human cold-sore virus) are common in winter and these are said to be often mistaken for machine problems. Wet, muddy conditions often result in a high incidence of chapped teats and/or calloused teat-ends. Alternatively, lesions may result from incorrect or insufficient emollient in the teat-dip, or separation of chemicals in the dip. Microscopic lesions can become infected and enlarged as a result of improper teat-dipping.

If milking clusters are correctly designed, well maintained, correctly applied and adjusted, then mean strip yields are typically less than about 0.3 L/cow. A problem exists if strip yields average more than about 0.5 L/cow. Undermilking causes bulk milk cell counts to rise because of the marked increase in the cell count of infected quarters. Furthermore, subclinical infections may flare to the clinical stage if cows are undermilked.

Completeness of milking can be assessed on commercial farms either by hand-stripping at least 10 cows into a bucket or machine-stripping them into a test bucket. Hand-stripping immediately after cluster removal has an added advantage: the relative amounts of milk remaining in individual udder quarters can be compared by measuring the milk volume, or estimated simply by counting the number of squirts from individual teats. If more milk can be hand-stripped consistently from left hind quarters, for example, then the problem is likely to be uneven distribution of the cluster weight between the udder quarters.

The most common causes of incomplete milking are: poor type or condition of liner; mis-match between the claw inlet and the short milk tube (causing partial closure of the short milk tube where this tube joins the claw); clusters that are too light; clusters that do not hang evenly on the udder because the connecting hoses are too long, too short, twisted, or poorly aligned in relation to the cow; or high milking vacuum levels.

The incidence of slipping or falling teatcups can be assessed by careful observation. A problem exists if more than 5-10 slips or falls per 100 cows milked require correction by the milker(s). The most common cause of frequent slippage is poor alignment of clusters in relation to the udder. Heavy clusters, uneven weight distribution within the cluster, or blocked air admission holes are other common causes of cup falling. A change to a more "stable" type of teatcup liner often helps to solve the problem.

Note the stage of milking when the falls mostly occur. Flooding clusters or milklines tend to cause slipping or falling early in milking. Poor cluster alignment, poor liner design or uneven weight distribution in the cluster are the most common causes of slipping and falling late in milking.

Note the time from cups on to cups off for at least 10 individual cows (or 10% of the cows in herds of more than 100 cows), then calculate their average milking time per cow.

Field studies in England, France and the USA show remarkably consistent results. On average, cows giving 10 L of milk per milking will be milked in about 5 minutes (give or take 0.5 min each way). Cows producing about 15 L per milking will be milked in about 6 minutes (plus or minus 0.5 min). The conclusions: 1) add 1 minute to the mean milking time per cow for each 5 L increase in mean milk yield per milking; 2) slower average milking times per cow may indicate problems with milking equipment or with milking management.

The most common pulsation faults include cracks or splits in the pulse tubes, foreign material (dirt, grit, straw, feed particles or insects) under the pulsator valve seats or lodged in the air inlet ports.

Listen closely to each pulsator as a first check for uniformity between units. The sound of air entering the external air port should be regular and intermittent. This simple check is made more sensitive by partially covering the pulsator air port with a finger. A continuous hiss indicates a leak (usually grit or dirt) under the pulsator valve seat. Check that the pulsator air filter or air port is absolutely clear.

Feel that all liners are at least opening and closing fully in a pulsation cycle by turning on the vacuum shut-off valve to each cluster in turn and inserting a thumb into each teatcup in turn. If carried out systematically, this simple test is a good guide to uniformity of liner action between pulsators.

Connect a vacuum gauge to one short pulse tube in each cluster via a suitable T-piece and observe the movement of the gauge needle. The needle should move cyclically between the full milking vacuum and full atmospheric pressure. While it is not possible to estimate the time or percentage of each phase of the pulsation cycle with this simple test, it is easy to check that the gauge needle covers the full range of pressure change and remains stationary at the full atmospheric pressure level for a brief but perceptible period (only about 0.15 to 0.2 seconds) in each cycle.

The subtle effects of inadequate pulsation may be the single most important cause of poor milking performance and machine-related mastitis problems. If there is any doubt about the results of these simple tests for effective pulsation, then call in a qualified technician for a complete evaluation.

2. Vacuum Regulation.

Farm vacuum gauges often are inaccurate. Sometimes the indicator needle sticks and it will not move above 45-50 kPa to indicate a high operating vacuum if the regulator malfunctions. Tap the face of the gauge to check for a sticking needle. Check the reading on the farm vacuum gauge and, preferably, check the operating vacuum with a separate vacuum gauge of known accuracy.

The vacuum pump should have sufficient reserve capacity (known as the Effective Reserve or the Manual Reserve) to cope with accidental air admission through the teatcups during milking. The adequacy of reserve pump capacity can be estimated in the following way. Note the vacuum level (preferably, in or near the receiver) with all units shut off. Then, open the vacuum shut-off valves to one unit (or two units in systems with more than 32 units). If the vacuum level does not fall more than 2 kPa, then the Effective Reserve is likely to be adequate. If this test is made under the same conditions each month, and the vacuum level recorded for 1 or 2 clusters fully open, then gradual changes in reserve pump capacity due to air leaks, pump wear or regulator malfunction can be monitored systematically. If in any doubt, then call a qualified technician.

The vacuum regulator requires regular checking, cleaning and maintenance to maintain its designed level of performance. Listen closely to the sound of air entering the regulator when the plant is operating but with all units shut off. Then, open the vacuum shut-off valves to one unit (or two units in systems with more than 32 units) and listen closely to the regulator again. It should be possible to detect a great reduction in the hiss of air entering the regulator. If not, then check the regulator filter and clean if necessary. If cleaning does not improve the regulator sensitivity, then call the company service technician.

Liners should have a barrel diameter about 1 or 2 mm less than the average diameter of the teats after milk letdown. Liners with a diameter of about 22 mm at mid-barrel are fine for typical Friesian herds (or about 23 mm for herds with unusually large teats). Liners should be designed to fit the teatcup shells. The mouthpiece should not be distorted by the cup. Liners should fit firmly to prevent twisting in the shells.

Liners should have no cracks in the short milk tube connecting to the claw, and no surface crazing or swelling evident on the mouthpiece lip or inner barrel. Visually inspect at least 20% of the liners and short milk tubes for cracks or splits.

Liners should be long enough to collapse below the teat. Pulsation fails if the liners are unable to collapse because the teat penetrates too deeply. The minimum effective lengths of liners, made of natural rubber or synthetic rubber, should be: 135mm for liners with 21-22mm bore at mid-barrel; 140mm for liners of 23-24mm bore.

The air vents in the claw or teatcups should be clear and unblocked. The hole in the claw is usually about 0.8-1.0 mm in diameter. Teatcup air vents are about half this size, so they will each admit 25% of the air that flows through the larger claw vent. Claws that have an effective volume of at least 120 ml below the milk inlet nipples help to reduce possible problems of flooding and cross-contamination between the teatcups within a cluster.

Hoses\tubes should be inspected for wear, cracks, tears, or change in cross-sectional area due to kinking, distortion or swelling due to fat absorption. Most common faults include reduction in cross-sectional area of milk hoses (due to kinking or bending near the milkline inlets) or of short milk tubes where these join the claw inlets (due to age or mis-matching) or cracks and splits in short milk tubes and pulse tubes. Large (16 mm bore) unrestricted milk tubes and droppers are recommended for high-producing, fast-milking herds.

Milk inlets from each cluster should enter the upper third of the milkline. Large (16 mm) unrestricted milkline inlets are recommended for high-producing, fast-milking herds. Milklines should be mounted as low as practicable (and never more than 2 m above the cow platform). The recommended system vacuum level depends mainly on the height of the milkline above the cow platform. Typical vacuum settings are 42-45 kPa for milklines mounted at or below platform level, 45-48 kPa for mid-level milklines, and 48-50 kPa for higher milklines. The recommended vacuum setting depends also on the number and type of extra components fitted between the cluster and milkline.

The most common milkline faults on typical farms are inadequate size, and variable slope or flat spots. Slope should be measured at several places along the milkline using a spirit level. The milkline should have a uniform slope towards the receiver with a minimum fall of 1% and preferably 1.5%. The greater slope increases the liquid-carrying capacity of the milkline, so reducing the risk of milk slugging, and can improve the drainage of cleaning solutions. The effective carrying capacity of milklines can be increased by raising the slope to 2-2.5%. For practical purposes, slopes greater than 1.5% are not recommended unless the cow platform can be sloped in the same direction as the milkline.