A machine to make up doses of semen in a container comprising welded thermoplastics films that can be opened by hand without using instruments in order to insert therein an insemination probe includes a tubular needle having a nozzle over which is threaded a cleaning ring to prevent coating of a region to be sealed by welding with semen and to keep the walls of the thermoplastics films dry after filling the dose with semen. The sealing weld is made by a device having inverted U-shape jaws. An incision perpendicular to the branches of the U-shape is made at the same level as the latter by an incision device including an orientable blade.