Benefits of the right selection and maintenance of teat cup liners include:
- Improved animal health - ensures teats are not damaged leading to issues with mastitis.
- Increased milking efficiency - the right liners will help to ensure clusters stay on and cows are not slow to milk.
- Reduced stress on animals - ensure the liners are not causing pain which will lead to cow discomfort and animal handling issues.
A good teat cup liner will:
- Provide an airtight seal at both ends of the shell;
- Provide a mouthpiece and barrel of a size that will fit a range of teat shapes and sizes, minimising liner slips and cluster falls and damage which can lead to mastitis;
- Milk out as quickly and completely as possible, minimising teat congestion, discomfort, and injury;
- Be easily cleaned.
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An array of different liners.
Liners are commonly described as wide, medium or narrow-bore depending on their internal diameter relative to the average teat size for a given herd. A wide-bore liner is at least 1 mm larger than the mean teat diameter measured at the mid-point of the teats. A narrow-bore liner is at least 2mm smaller than the mean mid-teat diameter of the herd. Talk to experienced suppliers and technicians to help decide on a size that suits your operation.
The majority of New Zealand liners have a cylindrical barrel, but square, triangular and oval designs are starting to appear on the market.
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Anatomy of a teat cup (liner and shell).
A cross section of different liners to show the length, size and shape.
The appropriate effective length (EL) of the liner depends on the range of teat sizes in a herd, and on the liner bore (see table below). Wide-bore liners need a longer EL because the teat penetrates further into them.
NZ Milking Pump Trade Association (MPTA) technicians have access to tables showing the effective lengths of different commercial liners and how to measure the effective length.
Correct mounting tension is essential to give proper pulsation squeeze on the end of the teat. Liner tension is determined by the size of the liner in relation to the shell. Conventional rubber liners should have 5% to 16% stretch. Liner tension can be checked by measuring the shell, then the tension ring where it fits the shell.
Liner bore at mid-barrel (mm) Minimum effective length (EL)(mm) 21-22 135 23-24 140 >25 145 -
Changing your liners when they are worn out, or if they do not fit the shell properly, will make money not cost money. The purpose of this calculation is to decide whether a liner is capable of working effectively.
NB. This is only one of four checks needed to decide whether or not a liner is worn. See later.
Procedure: You will need the template below, a ruler, your shell, a liner and some callipers. Measure the following and write the results down:
The length of the shell.
The length of the shell.
The tension length of the liner.
The tension length of the liner (barrel length from the shell seat beneath the skirt to the edge of the appropriate tension ring, where it fits against the shell).
Liner tension ring and shell hole measurement.
Liner tension ring and shell hole using the ruler for the shell and - if you need the greater accuracy - callipers for the liner.
A Shell length. A= B Liner tension length. B= C Outside diameter of liner tension ring where it passes through shell hole. C= D Inside diameter of shell hole. D= Calculations Liner stretch calculation = ((A-B)/B) x 100 5-16% is Ok. Liner constriction calculation = C - D 2-5 is Ok.
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How do I maintain my teat cup liners?
A good cleaning system with regular hot alkaline washes is necessary to maintain liner performance. Poor cleaning can result in faster surface deterioration and bacterial growth.\
Liners should be removed from jetter wash systems after cleaning. Leaving liners on any type of jetter between milkings will not allow the system to dry and can increase bacteria growth. Liners left hanging on button style jetters can distort the mouth-piece, increasing slip and reducing liner life.
Liners should not be re-tensioned by pulling them up to a second tension ring after half of their life, they should be replaced as they are worn out. Re-tensioning will only improve milking for a short time. Over-tensioned liners may lead to teat end damage.
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Liner slip.
Liner slip is inconvenient and can have a negative impact on milk quality. It is often due to causes other than the liner itself.
Factors influencing liner slip and recommended action Factor influencing liner slip Action Unsuitable choice of liner Select a liner which suits your herd and their teat size. Incorrect vacuum levels Maintain vacuum levels in the proper range for your milking system. Inadequate vacuum pump capacity and line sizes, excessive system leaks, long sagging milk tubes Be sure all components of your milking system are properly sized. Keep milk lines as low as practical (always < 1.8m). Shorten the stainless steel part of the long milk tube to end 500-600 mm above the cow platform. Poor regulator, or variable speed drive response An insensitive vacuum regulator (or variable speed drive) can result in extreme vacuum fluctuations. Keep it clean and serviced. Poor cluster alignment The cluster must be well aligned with the udder to achieve a good seal between the teat and the liner. Shorten the long milk rubber so that it doesn’t sag, helping the cluster to hang evenly. Don’t make it so short that it pulls the cluster out of alignment. Shift the milk line if it is not possible for the clusters to sit squarely under udders. Twisted liners Liners that are twisted inside the shell prevent the teat from entering the liner properly, resulting in a poor vacuum seal. Make sure the index mark on the liner head and short milk tube are aligned. Take care liners are not twisted when placing cups on jetters. Light quarters Light quarters often cause air leaks between the teat and liner. Cluster weight Check that the cluster weight is not too heavy.
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An old liner beside a new liner showing liner stretch from use.
- The expectation that liners should last a full season does not take into account the growth in farm sizes in recent years. Liner life expectancy must be calculated for each individual farm based on herd size / number of clusters and milking frequency.
- As a general rule of thumb, if you notice a distinct improvement in milking performance after replacing the old liners, you have probably used the old ones too long.
- Old liners can also cause plant hygiene problems as the internal surfaces of older liners are more likely to become cracked and harbour bacteria.
- With older liners there is also an increased risk of the liner splitting. If this occurs milk will be able to flow between milk side and air side of the milking machine, potentially resulting in milk quality downgrades.
- Liners should be replaced after 2500 cow milkings.
Liner replacement guide.
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Visual checks
Check the liner for perishing, cracks and splits.
Do monthly checks of liners and short milk tubes for cracks and splits. Early detection of split liners can be improved by fitting clear (normally PVC) short or long pulse tubing.
A teat ring caused by a vacuum in the mouthpiece chamber.
- Liners should have no cracks in the short milk tube connecting to the claw and no swelling on the mouthpiece or inner barrel.
- Check liners for twisting in the shell.
- Feel inside the barrel, it should be smooth and have no black residue.
- Check the liner for perishing, cracks and splits.
Performance checks
Regular occurrence of any of the following may highlight an issue with teat liners or milking machinery:
This ring being on constant vacuum is responsible for holding cups on. Unusually pronounced rings on cows' teats indicates overmilking or too high a vacuum level.
- cluster slips or falls (should not exceed 5 slips per 100 cows);
- poor teat condition in the herd. There should also be no rings at the top of the teats, no teat discoloration after milking and no teats should appear swollen;
- irritable cow behaviour during milking;
- incomplete milking out of cows;
- slow milking times for cows.
