An intraruminal device has hinged wings (6) which lie along the body of the device during administration to the animal but which are urged outwardly by a spring (14) acting on a piston (12) shortly thereafter. The wings (6) are locked in the extended position: the piston (12) prevents them returning to the starting position, and T-bars (10) prevent them continuing to an "arms-over-head" position. The locking means may comprise a latch. The spring (14) may be replaced by a water-swellable polymer which expands on contact with rumen fluids. The device is used to administer drugs or minerals to the rumen of a ruminant over a prolonged period.
