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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.
Kittens can be spayed as early as 6 weeks; however, ideally they should be spayed between 8 weeks to 6 months. That is called Juvenile or Early spay.