An animal pen according to the invention comprises an access wall spanning the width of the pen between two side walls. An access door in the access wall is hinged to a vertical hanging post and closes against a vertical slam post. A first of the posts, which may be the hanging post or the slam post, is supported at its top end not by a door lintel extending between the hanging post and the slam post but by a diagonal brace member extending between the top of the said first post and the top of its adjacent side wall, and the second of the posts is supported either by being located at a junction between the access wall and its adjacent side wall or by a similar diagonal brace member extending between the top of the said second post and the top of its adjacent side wall.