Abstract: A pen for domestic animals, preferably sows, the pen having a size such that one of these animals can stay in the pen. The pen has a rear gate which is hinged horizontally and positioned above the animal's back in the open condition. The rear gate has a release mechanism for releasing the rear gate from the closed condition. The release mechanism is adapted to allow releasing of the gate from closed condition by a rearwards directed push by the animal in the pen against the rear gate. Furthermore, the release mechanism includes a pivoting arm on the rear gate, where the pivoting arm is connected with a barb for releasing the barb from engagement with a fitting when the pivoting arm is moved rearwards.