At whatever age spaying is done, it will reduce estrogen levels. So, although it is probably best to spay rats at a young age-between 3 and 6 months-it is probably also beneficial to have older rats spayed as well. However, the older the rat, the more likely that tumors, especially a pituitary tumor, will already be forming. Probably, spaying should be done before the rat is a year old to be assured of preventing tumor formation.
If you have a rat that already has a mammary tumor and you decide to have it surgically removed, you should also consider having her spayed at the same time to help prevent future tumors. Other benefits of spaying that shouldn’t be overlooked are the elimination of uterine infections and cancer of the uterus and ovaries. Spaying is one of the best ways to ensure your female rats live as long as possible.