 Research in the 1960s proved that female animals permitted to reach sexual maturity prior to being spayed were susceptible to a higher risk of mammary cancer than those animals spayed prior to their first cycle.As a result, the recommendation was revised to perform surgeries just prior to the average anticipated age for the first cycle, 4 to 6 months for cats and 6 to 12 months for dogs.Research from the 1990s and early 2000s suggests that it is safe, and maybe even desirable, to perform sterilization surgeries prior to sexual maturity and as early as 6 weeks old (but no less than 1 kilogram [2 lbs]).