Vented liner (10) for milking plants comprising a head (14) incorporating an orifice (19) constituting the mouthpiece for the teat (18) of the animal being milked, a body (15) comprising the central portion of the vented liner (10) in which the teat (18) is housed during milking, a milk tube (16) comprising the portion of vented liner (10) located opposite the head (14), an insert (20) which can be inserted within the head (14) of the vented liner (10), the said insert (20) comprising a shaft (23), a head of the insert (22) connected to the shaft (23) and a through-hole (26) made longitudinally in the shaft (23) and passing through the head of the insert (22) and the shaft (23) to allow a controlled constant inflow of air into the head (14) of the vented liner (10), a thread (24) capable of being screwed onto the head (14) of the vented liner (10) penetrating the rubber of which the liner is made being provided in the shaft (23), and/or the through-hole (26) comprising an upper portion (28) of constant diamet
