It is called Delvosterone, and you give it about a month before they are due in season (or even when they come in if you don't know when they are due) then after three months, then after four months then after five months, and thereafter every five months. There is a very minor risk of pyometra, but no more than in a bitch that has seasons. There is a risk they may not come into season, or have very odd seasons. I have had my two bitches done now for about three - four years, one of them was not jabbed when due in January, and she came in season last week, with a view to mating her. My friends Rottie came in about a months after her jab would have been due. We always used this for greyhounds to keep them racing, as they have to be off the track for three months after a season in case they come into milk and are not properly fit to run. We never had a problem getting them in whelp after being jabbed for several years. It can also be used to stop them if they have come in season, or to stop the symptoms of a phantom pregnancy. Some vets will not advise it, but many do - have a chat with your vet. It costs me about �16 per jab, and I have an arrangement with my vet where he doesn't charge me for the consultation, as it is an ongoing treatment and he doesn't need to examine them.