Abstract: The present invention provides pharmaceutical or veterinary implants which, when subdermally administered releases a peptide or protein in a substantially continuous manner. The implant includes the peptide or protein and an excipient encased within a polymeric coating which is permeable, swellable and, at normal physiological pH, is non-rupturing, non-dissolving and does not degrade over the useful life the implant. The coating forms a release rate limiting barrier. All of the components used to make the implant are of a biocompatible nature. The implant is particularly useful for the sustained release of proteins or peptides for regulating the hormonally controlled reproductive cycle in sheep.