The teat cup has direct contact with the cow's teat. Nothing must go wrong here, otherwise the milking process is immediately adversely affected.
During milking, the teat cup opens and closes by pulsation.
When the teat cup is open, a vacuum is created, causing the milk to flow out of the teat.
When the teat is closed, there is pressure on the teat. The interaction between opening and closing causes blood and lymph fluid to flow from the teat back into the cow's bloodstream as it closes.
Partly due to improper teat cup selection and/or milking system adjustment (especially too much pressure), calluses can form at the teat end.
"Worn or old teat cups" still do their job.
As long as they are not damaged, you usually only notice the wear by a slower milking rate.
Oddly enough, problems with milking often start after a (too late) replacement of the teat cups!
After a (late) change, cows react very differently than you would expect. The milking process even deteriorates.
The reason is obvious:
The liner of the new teat cup acts differently on the teat than the "worn" old one.
While the old one lacks resilience (making the nipple and teat canal smaller), the opposite is true with the new one.
Cows have to get used to this. They experience it as if "another calf" is sucking, the sucking behavior is totally different!
With old teat cups, there is a lower peak milk flow and the milking rate decreases.
However, the fluctuation in vacuum can increase. Thus, it takes longer to milk the cow.
Using the same teat cups for too long also makes the material rougher. This can have a negative effect on milk quality.
The lifespan of teat cups also depends on the number of milkings.
Replace teat cups promptly to avoid udder problems and problems during milking.
Ask your milking equipment supplier for advice.
Source text and photo Ronald Rongen