Reverse pressure gradients across the teat canal related to machine milking.

Miniature pressure transducers were inserted through the udder cistern wall of 10 cows and placed into the teat cistern and, in addition, beneath the teat end. Data were sampled every millisecond and collected during 59 sequences of manual teat handling pre- and postmilking, 575 attachments, 384 sequences of 30-s milking, and 623 sequences of detachment. Attachment and detachment were mainly done during overmilking in short sequences lasting 8 to 20 s. Reverse pressure gradients across the teat canal occurred during manual teat handling (54%), attachment of the milking unit (29%), milking (1%), and detachment (26%). Overall risk included empty teats. Risk factors at pre- and postmilking teat handling were the compression of teats and the following movement back to normal shape. When the diameter of the mouthpiece orifice of the liner was larger than the teat diameter, the frequency of reverse pressure gradients at attachment was halved compared with attachment of more narrow liners. The method of attaching the milking unit on empty teats without the risk of creating reverse pressure gradients was not identified. Reverse pressure gradients in empty teats may be avoided during detachment of liners if the mouthpiece orifice diameter is greater than the teat diameter. Detachment with the liner in open position reduced the risk of reverse pressure gradients compared with that from the closed position.