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While spaying is traditionally recommended for kitties between 4 and 6 months of age, spaying as young as 8 weeks old is considered safe, according to Cat Channel. Many animal shelters actually spay kitties prior to adopting them out at this age.
One can spay a mother as soon as the kittens or pups are weaned, (5 to 6 weeks for kittens and 4 to 5 weeks for puppies) and because of the risk of pregnancy this should be done.