According to one aspect of the present invention there is provided a substance delivery device (1) capable of insertion into a body cavity of an animal, including delivery apparatus (11) capable of actively being controlled to deliver a substance to an outlet, and retention apparatus (2, 3) capable of retaining the substance delivery device within the body cavity of an animal. In one embodiment, a microprocessor (18) can be remotely programmed to enable control over the delivery device after it is placed in the animal. The microprocessor (18) can also communicate with an external device to enable the operation of the delivery device to be determined. The invention may also include sensors to monitor the environment around the delivery device, to determine when a substance should be delivered into the body.