The bag comprises two flexible sheets (11) attached to each other by a weld area delimiting a pouch having a predefined volume when said bag is filled, said pouch being designed to contain a dose (27) of said diluted animal semen having said predefined volume. The surface (30) of each of said flexible sheets (11) faces said pouch (14) which is part of a layer (35) of weldable thermoplastic material. For one or preferably for each of said sheets (11), said layer of weldable thermoplastic material (35) comprises triclosan； and the ratio between said predefined volume of said pouch and the sum of the areas of the surfaces (30) of said sheets (11) facing said pouch is between 0.3 ml/cm2 and 0.5 ml/cm2. The system comprises such bags and an antibiotic-free dilution medium.
