Liners

The teat cup liner is the only component of the milking machine that comes into contact with the cow's teat. It has a large influence on milking performance, udder and teat health.

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.

How do I choose the right teat cup liner?

Choosing a liner is a compromise. One must consider the milking machine, its settings and very importantly, the cows.

Ultimately, if the proposed liner fits the milking equipment, it can be compared in the milking performance of your cows alongside other liners aiming for fast, efficient milking without any 'ill' effects.

Even then, a better performing liner may warrant some change in equipment.

• the performance of cup liners is heavily influenced by the design and management of the whole dairy. Liner slip in particular is often not due to a problem with the liner itself. To optimise the milking process, milking machinery should be assessed in its entirety. Liners need to be carefully selected to suit the herd and machinery, and changed regularly.
• Liners are commonly classified by their barrel size and shape, and by the material and/or method of their construction.
• There are many liners available in New Zealand, the diameter of their mouthpiece lip ranges from 20-25 mm, the mid-bore of the liner barrel from 20-28 mm, and the effective length of the liner from about 120-170 mm (depending on shell length).
• The majority of liners available in New Zealand are made from Food Grade Synthetic rubber.

Method of construction and dimensions

Liners may be made in either 1 or 2 piece designs. A 2 piece liner has a separate short milk tube. Most New Zealand farmers choose 1 piece moulded liners, as they are easier to assemble and simpler to change when due for replacement.

Barrel size and shape

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.

An array of different liners.

Liner length and tension

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.

Anatomy of a teat cup (liner and shell).

A cross section of different liners to show the length, size and shape.

Measuring liner stretch

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 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 using the ruler for the shell and - if you need the greater accuracy - callipers for the liner.

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.

Preventing 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.

Replacing old liners

Liners should be replaced as they are worn out, not re-tensioned. Re-tensioning will only improve milking for a short time and over-tensioned liners may lead to teat end damage.

• 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.

Changing to a different type of liner

When changing the liner type it is important to get a good match between liners and cup shells, and also with the rest of the dairy set up.

Most milking equipment companies provide guidelines for correct matching of their own particular brands, and technicians usually have access to a collated set of MPTA specifications from different companies.

Important maintenance checks on my teat cup liner

Visual checks

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.

• 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.

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:

• 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.