That's the term I found here:
http://www.archive.org/stream/dictionnairetec00vivagoog/dict...

and in my own Dictionnaire de la Métallurgie by Raymond Coël:
mère (gueuse): sow, sow channel
mère-gueuse: sow, sow channel

In Termium, at "mère", I found
trumpet assembly
descente de coulée
OBS – --the vertical refractory tube encased in a metal shell which is used in bottom pouring. It consists of a trumpet, a number of guide tubes and a bottom guide.

This is what my dusted-off paper copy of Ernst's technical dictionary offers (and also 'trumpet assembly') and I found this US patent to support it:

http://www.patents.com/us-3865177.html
The present invention relates to a method and system for the bottom-casting of ingots, slabs and the like, in which casting is effected in moulds positioned on a casting platform with respective mould gates located above and in communication with outlet openings opening out in the casting platform, which outlet openings communicate via distributing channels with a vertically extending teeming gate arrangement, from which the moulds are filled gravitationally with molten metal, i.e., with the metal subjected only to atmospheric pressure, to the desired level by free communication with said arrangement in accordance with the principle of communicating vessels.

Known methods and apparatus for casting ingots, slabs and the like require excessive space and, moreover, produces a relatively large quantity of spillage, commonly known as return metal, which reduces the capacity of such apparatus. According to one conventional bottom-casting method, there is first arranged a system of molten metal supply channels, whereafter moulds intended to receive the molten metal are placed over the outlet openings of the supply channels in register with the mould gates. Centrally of the system of supply channels there is normally arranged a teeming gate, to which the molten metal is charged from a ladle or teemer. The molten metal teemed into the gate passes through the gate and into the system of supply channels, up into the moulds through the mould gates. When the desired level of molten metal in the moulds is reached, teeming of the metal into the central gate is interrupted, the level of molten metal in the central gate than coinciding with the level of the metal in the moulds in accordance with the law of communicating vessels, and the molten metal caused to solidify both in the moulds and in the system of channels and the central teeming gate. When the metal in the moulds and the supply channels has solidified, the sprues connecting the solidified castings is broken, e.g., by twisting off the sprues in the mould gates, whereafter the castings are removed from the moulds, by applying one of the well known stripping methods.