contracption for nursing queen

Question
A stray female cat  moved into my house about 3 weeks ago. She gave birth to 4 kittens 14 days ago. I would quite like to keep the 5 of them.I understand she may go into heat again before she is finished nursing the kittens. Even now there is a tom cat waiting outside. Can a vet administer contraception until she can be spayed?  

Answer
Hi Margie.  There is a contraceptive called megestrol acetate, which can be given as an injection or orally, that will delay estrus cycles until you can have her spayed.  It does not generally interfere with lactation in nursing mothers.  However, it is not without the risk of side effects.  They may include weight gain and high blood sugar, but also could include such serious side effects as mammary tumors, diabetes and pyometra (a serious infection of the uterus) if used for more than a couple months.  So when possible, it's best to keep her indoors and away from tomcats, but if this isn't feasible, then megestrol acetate may be used until she's weaned her kittens.  Some vets feel it's better to spay even while the kittens are nursing than to use megestrol acetate at all.  This is actually common practice here in the U.S. while working with feral cats.  Certainly some options to talk to the vet about!  Thanks for taking in these kitties, and enjoy your little ones!