“The teat should look much the same before and after milking. Teat distortion, the pinching or wedging of the end, a ring round the top of the teat or a teat turning a blue-purple colour all indicate a possible liner problem,” he said.
“Uncomfortable cows are likely to be restless, stamp their feet and kick the clusters off, particularly heifers.”
After milking, the udder should have milked out cleanly and completely, and be wrinkled.
“A fleshy unmilked-out udder shows the liner is leaving lots of strippings. This can affect milk production and somatic cell counts, depending on the severity of the problem.”
He said the liner should sit firmly on the teat without slipping down and squawking or letting air in around the top.
“Liner slip is annoying to the milker and slows the milking rate of the cows. Accept no more than five slips per 100 cows.
“Aim for all cows, apart from those with teat damage or deformed udders, to be milked out within a seven to eight minute row time which is 10 litres in five minutes, 15 litres in six minutes.”
He said when changing liners, farmers should think about what problem they are trying to solve.
“Is it cow discomfort, is it not milking out, is it slippage, is it slow milking?”
Although cows in a herd might have many different shaped teats, Wheeler said it was about finding the best compromise.
“Firstly, fix any cluster alignment issues and ensure the vacuum level is correct, then consider the cluster weight and only then attack the liner problem.”
The mouthpiece of the liner is designed to allow the teat to enter the liner and then seal around it.
If the mouthpiece is too small teats will be left with ring marks around them and quarters will fail to milk out. Too large a mouthpiece and the cups will slip from the udder.
If the mouthpiece is too soft it will collapse into the cavity and cause slippage, too stiff and cow comfort can be a problem.
The mouthpiece cavity forms a vacuum chamber to stretch the teat to grip the liner so there should be some swelling in the teat but not excessive swelling. If the mouthpiece cavity is too small then there will be slippage, too large and there will be poor milk out and discomfort.
The barrel is designed to carry the weight of the cluster so the heavier the cluster the wider the barrel liner. Ideally, although opinions vary, it should be one to two millimetres wider than the teat.
It partly seals against the teat and provides pulsation via the vacuum changes between the liner and shell.
The liner must have tension to provide the squeeze that reduces teat swelling during milking. Thin-wall liners need more stretch than thick-wall liners to give them the same ability to squeeze the teat. Depending on the liner wall thickness, the stretch should be 5-16%.
Wheeler said because front teats were different to back teats, farmers should possibly look at two different sets of liners for each cluster if cupping between the back legs.
“Back teats are usually shorter and thicker than front teats and back quarters contain one and a half times the volume of milk compared with front quarters.
“As well, clusters tend to pull down on front quarters and push up on hind quarters aggravating the slip, increasing crawl on the back and stopping quarters milking out properly.”
Liners also needed to fit clusters properly and jetters.
Wheeler suggested farmers try new liners before they bought them, placing two of them on the diagonal on several clusters making sure the milk tubes were the same length and seeing how they performed during a number of milkings.
“About 10 seconds after the cluster has been put on, pull down firmly but gently on the front shells, supporting the claw in the other hand. A liner that is likely to slip will slide down the teat.”
He also said to check the milking rate and whether all quarters were milked out.
When the cups were removed the four teats should be compared.
“The more uncomfortable liners will distort teats and they may be swollen and discoloured particularly at the top of the teat. Turn the end of the teat upwards and it should be more or less round rather than wedge shaped.
“Blueness on the teat will show that it’s been stretched to fit the liner which leads to poor cow comfort and poor milk out. The blue is due to the blood not circulating and becoming de-oxygenated.”
New Zealand’s mainly synthetic rubber liners had a life of about 2500 milkings based on manufacturers’ recommendations, but Wheeler said several other factors also shortened or lengthened a liner’s life.
“It’s also about the number of flexes or collapses that happen during milking. For example, a farmer milking 10 rows with the clusters left on for six minutes per row with a pulsation rate of 60 pulses a minute, then the liners will open and shut 3600 times per milking. But a farmer with 15 rows of cows milking for six minutes a row at 60 pulses a minute will have liners that are opening and shutting 5400 times per milking.”
He said liners that were not kept clean would not last as long.
“The plant wash system needs to include a minimum of two alkali washes per week recycled for five to seven minutes to ensure the removal of all milk fat.”
Cows kicking off cups causing them to hit concrete or pipework could split the mouthpiece. Rigid jetters, or leaving the cups on the jetters after washing, also caused damage.
“Thicker walled liners do last longer but it is thought now that liners with thinner walls perform better and are worth the financial cost of a slightly reduced life.”
