The old wives' tale about female cats being safe from pregnancy as long as they are still nursing kittens is simply not true. Most cats will have an estrus cycle (the technical name for heat) within six to eight weeks after giving birth. In rare occasions, a cat will have an estrus cycle within a week after her kittens were born.
Estrus is described as the period of receptivity to mating, and is linked with the production of estrodial (a type of estrogen) produced by ovarian follicles.
It is not to be confused with menstruation in human females, and you will rarely, if ever, see any signs of blood, although occasional mucous discharge may be evident.
Female cats are induced ovulators, which means that ovulation does not take place without mating or manual stimulation. If the female cat does not mate during estrus, hormonal levels will eventually drop off, and the estrus cycle will cease, until it repeats itself in another two to three weeks.
When Can Cats Become Pregnant?
In more detail, both male and female kittens can reach sexual maturity between four and six months, so it is entirely possible a kitten could impregnate his mother. This is potentially dangerous both for female cats and for her kittens. Several repeat pregnancies with only short periods between give added burdens to a cat's health. Bearing kittens, giving birth, and nursing them can sap a cat's physical resources, leaving her malnourished and exhausted, eventually.
Ovulation will usually occur within 20 to 50 hours after mating, and the eggs are viable (capable of being fertilized) for approximately one day. The eggs are fertilized in the oviduct, and then make their way to the uterus via the uterine horn, implanting in the uterine lining within 10 to 12 days.
And a female cat's litter may have kittens from multiple sires. On the street, a female cat in estrus may mate with two or more male cats over the length of the estrus cycle - up to 21 days, with an average of seven days.
Responsible breeders of purebred cats keep this in mind, and limit the number of litters a given female cat will have, and keep a reasonable gap of time between litters, to enable her to completely wean her kittens and to recover her optimum health. At some point the female cat will be retired, at which time she will be spayed, to prevent any further pregnancies, and to allow her to enjoy her senior years, so richly deserved.
Reasons for Neutering and Spaying Cats
Unless your cat is a purebred, there is no legitimate reason to allow her to continue having kittens. The reality is that although it has been improved by educating the public on the importance of spaying and neutering pets, we still have a huge cats and dogs overpopulation problem in the United States.
Since kittens are so popular, the majority of people who adopt, will adopt kittens, leaving the adult cats behind at risk of euthanasia. The more kittens available, the risk of their escaping euthanasia becomes greater.
Once she's had kittens, it's best to get a female cat spayed and any male kittens neutered. They will both be happier and will make better pets in the long run.