a biodegradable intra vaginal device for insertion into the vagina of an animal useful for herd oestrus synchrony purposes , the device is intra vaginally insertable , intra vaginally retainable and withdrawable by virtue of its ability to change its geometry yet is formed at least almost exclusively from a cyclodextrin and progesterone impregnated moulded matrix of a polyester polymer ) or a starch - like polysaccharide polymer . there is preferably a loading of progesterone of from 0 . 1 to 3 gms . the surface area of the impregnated matrix is preferably from 15 to 200 cm 2 . related methods and uses also form part of the invention .