Liner Slippage

Liner slippage

Liner slippage is recognised as an important potential source of mastitis infection. The obvious signs of liner slippage - squeaks and squawks from one or more teatcup liner as the cow is being milked - indicate air entering the liner through the top of the liner mouthpiece, when the mouthpiece loses contact with the teat skin, and the teatcup fails to milk properly and drops down the teat.

This slippage is indicative of the vacuum loss and impact forces that occur due to pressure differences in the clawpiece and teatcup liners caused by the air escaping into the liner, where reverse milk flow can occur and milk droplets are forced at high speed back up towards the teat. This is likely to lead to the teat canal being impacted with significant force by potentially-infected milk from other quarters, or milk remaining in the liner or clawpiece from previous cows that have been milked.

The teatcup liner should, by design, ensure an airtight seal at the base of the teat to minimise liner slippage, with a soft, flexible liner mouthpiece. Liner slippage can be caused by a variety of factors:

  • Worn or perished liners.
  • Milking cows with very wet teats.
  • Low vacuum levels or high vacuum fluctuations during milking.
  • Cows with particularly large, small or misshapen teats.
  • Cows with large udders (with a loss of udder suspension from ligament damage) that result in awkward teat angles.
  • Heavy cluster weights, sometimes caused by milkers placing weights on the clawpiece to facilitate 'machine stripping' (for quicker milking).
  • Incorrect liner design.

Liner slippage tends to occur towards the end of the milking, which has a double implication - this is when the teat canal is at its most open and most susceptible to damage and penetration from infection, and also there is a lack of milk remaining in the udder to 'wash out' any potentially-infected milk entering through the teat canal.

There have been several developments in liner design that aim to minimise liner slippage, or the effects of liner slippage when it occurs. These include shielded liners - where a perforated shield is fitted in the liner to reduce the effect of impact forces, ball valve liners - which aim to stop the reverse flow of milk in the liner, and triangular-shaped liners.

The occurrence of liner slippage cannot simply be measured by the incidence of the symptomatic noises produced by the slipping liner; regular professional testing of the milking plant is important to control liner slippage problems.