A cat can be spayed as soon as it is no longer nursing its kittens. Generally, this is between 5 and 6 weeks after the birth.
A cat begins going into heat at the age of 5 months. This is the age when it can begin reproducing. Therefore, it is very important to have it spayed to prevent overpopulation. Once a cat has had kittens, it can be spayed as soon as it is no longer feeding the babies. For most mother cats, this is about 2 months. It can get pregnant soon after the kittens are weaned, so an appointment to the veterinarian should be made as soon a possible.